1.  Get the parts..  they can most likely be obtained from a local junkyard for $200-300 including caliper, rotors, rear struts, all mounting brackets and bolts, and parking brake cable.

MAKE SURE YOU GET THE CORRECT PARTS!!!!!
Nissan changed their design slightly, so many parts made after 9/90 will not work with parts made before 9/90.  Mainly, the calipers and caliper mounting brackets are different between the two models.

Now for the parts you will need:
1.  Rotors
2.  Calipers
3.  SE Rear Strut assembly  (either find ones with good strut inserts or replace them when you have everything apart)
4.  caliper mounting brackets, including the pivot arm.
5.  SE Parking brake cables.  (see instructions)
6.  SE brake hoses.  I would recommend buying new ones, but if you get some that are in good shape, that'll be fine too.  I suggest replacing the little copper washers on the ends of the brake banjo also.  there is one on each side of the banjo, for 4 washers total.  good luck finding the right ones though.. it's probably a dealer only item, but  you may be able to get them at a parts store.
7.  New cotter pins for the rear struts.  You can get these at any parts store. Common item.
8.  You do NOT need a new master cylinder for this project.  there have been rumors that the part #s are different for SE and GXE master cylinders.  I'm going to assume that's because the person looking up the parts numbers looked at an SE with ABS and a GXE without ABS.  When I had three different dealers look up the part #s for non-ABS SE Maximas, they master cylinder was the same.  Nevertheless, These brakes work perfectly fine in my car with the GXE master cylinder.

Tools?  Yeah, you'll need lots of those:
Small and large ratchets, 3" and 6" extensions for the small one.
Complete metric socket set and open-end wrenches. Namely 10,12,14,17,19,22mm sizes. You will also need a large socket to remove the center hub nut- I think it's a 28mm, but not sure.
Air tools are mighty handy and could/should be used when possible..
Misc screwdrivers
Spring compressors, pipe wrench & STRONG vice- for tearing down the OEM struts.
Rags.  lotsa Rags.
bar clamp or some other large clamping device- doesn't have to be strong, just about 1ft long. Even a 2ft piece of rope would work.

Okay, let's get started!

First, loosen the lugnuts on both rear wheels. jack up the back end of the car and place on jackstands..  support the car firmly, because many of the parts you'll be taking off will require LOTS of force to break bolts loose, and you'll be completely underneath the car for parts of the procedure.

Remove the rear wheels and place somewhere out of the way (you're going to make a big mess today and need all the room you can get!)

Drum Assembly Removal:
If you have the parking brake set, unlock it.  remove the rear drums.  Remove the entire drum assembly by unbolting the four 14mm bolts on the "back plate" of the drum assembly.  Use a 10mm wrench to remove the brake hose at the top-rear of the wheel well. The whole thing should be free from the strut now, except for the parking brake cable. You can now remove the parking brake cable from the drum assembly by pulling the lever out a little, then working the cable off.  If you can't do it by hand like this, you can pull the shoe loose and then remove the cable.  It doesn't really matter, other than it's more work and more loose parts.

Parking brake cable exchange:
Now, grab that clamp I mentioned in the parts list, and pull the exhaust as far to the side as you can.  You don't need to remove it, but you gotta pull it out of the way.

Once you get this done, grab a 10 and 12 mm socket, several extensions, and safety goggles and crawl under the car.  Remove both parking brake cables, starting nearest the drums and working your way up.  In order to get to the end of the brake cables, you'll have to remove several sections of the heat shield above the exhaust too.  You may or may not have to move the exhaust around to get them off.  you'll figure it out. :)
once both ends of the brake cables are loose, you can unhook them at the "T" in the cable, just behind the catalytic converter.  There is no need to unhook the cable from inside the car.

Since you're already under here, you might as well start the conversion process by replacing the cables with the ones from the SE Max. Install is exactly the same as the removal, except in reverse order.  All bolt holes will match up, and you'll be fine.  Reinstall the heat shields and everything, and you're basically done under the car.

Strut Removal:
Now it's time to remove the struts.  Go inside and wash your hands, or have a clean person come and help for a little while.  Removing the struts is best done with 2 people anyway.
    Remove the top portion of the rear seat.  parcel shelf and lower seat cushion are fine where they are.
    If you don't know how to remove the rear seat,  there are 2 bolts behind the armrest in the center, and one under each corner of the cushion, by where the seatbelt attaches back to the car.  Once those are out, grab the top edge of the seat and pull- HARD. If you feel around back there, you'l find two small spots that make good hand-holds.  use 'em.

    Now that you've got the seat out, remove the round rubber/plastic covers over the tops of the struts.  using a 14mm ratchet, break these nuts loose, but DO NOT remove them yet!  let your clean helper do this stuff, since it's all inside the car.
    Get out all your big tools and unbolt the parallel links, radius arm, and sway bar from the bottom of the struts.  this isn't terribly difficult, but does take a fair amount of sweat and elbow grease to do.  Air tools are VERY handy right now.
    Now the bottom of the struts should be loose.  It's time to have your helper loosen the 3 nuts at the top of the strut towers while you hold the strut up.  when all 3 nute are loose, the strut should drop out of the wheel well.

If you have aftermarket springs/struts, follow these next few steps.  If not, skip down to the next section.

Take one of these struts and it's SE equivalent into the garage and begin disassembly.  Start with the SE strut.
For Springs:
    Clamp the bottom of the strut in your vice, and loosen the nut that the top of the strut.  DO NOT REMOVE IT!!! Just break it loose. If you remove it now, you're going to send a loaded spring flying straight at your head.  Not good.
    Now, use the spring compressors and compress the spring (duh!).  remove the top of the strut, taking care to mark orientation of the top 2 pieces BEFORE you disassemble.  This is important and will save you lots of time, sweat, and cursing if you spend a few extra seconds now.  I would suggest using a paint pen or something to mark the pieces.  just draw an arrow in the same direction as the spindle at the other end of the strut.  (this is "out")
    Now remove the top portion of the strut that you loosened earlier and remove the spring and strut boot/bumpstop.

For Struts:
    Call your helper again, as he/she may be needed for this part also.  it took both Kaleb and I to do this because my vice was worn out and turned on my workbench.
    Get your pipe wrench and remove the large nut at the top of the strut- the one that holds the strut cartridge in.  I ended up having to use a 2ft cheater bar on this, while sticking a 3 ft bar in the clamps of the vice to keep it from turning.  Brace one hand at the top of the strut, just below the spring perch.  (Placing your hand here will keep you from mangling it should the wrench slip.)  using the pipe wrench, PULL the wrench toward you.  Never loosen anything while pushing it away.  (Should the tool slip, you risk shoving your hand into whatever is behind you, possibly breaking knuckles..  your head will aim straight for the part you're working on and you risk breaking your nose or injuring yourself somehow when your head slams into the work.  soooo, always loosen stuck parts by pulling towards you :).
    Once this nut is loose, pull it off the top of the strut and set aside.  use a small screwdriver and pry up the rubber seal along the outer edge of the cartridge.  If you don't do this, it will be EXTREMELY difficult to remove the shaft!  place the entire strut over a large bucket and SLOWLY pull the innards of the strut out.  if you don't do this, you'll spill oil everywhere and make a nasty mess.  Now, turn the strut over and dump the rest of the oil into a smaller container for later use.
    Remove the spring compressors from the SE spring.
    Take all the parts from the SE strut and place to one side.  It's now time to disassemble your GXE strut.
    If you've already got cartridge inserts (tokico, any aftermarket replacements) in your GXE struts, all the same applies above except the oil part.
    Re-assemble the SE struts with the springs and internals of your GXE struts.  Take care to line up the spring and top section correctly and Don't forget to install a dust boot!  If you're not doing anything else, at least replace the worn out SE strut boot with a new one.

You should now have your "new" SE struts with correct springs and shock inserts in them.  It's time to mount them on the car.

Strut Installation:
Call your helper back in and have them help you install the strut in the car.  it's the same thing as removal, only in the reverse procedure.
Bolt everything back down to correct torques. (If I knew them, I would tell you.  I just cranked everything tight and went on my way. (Shhh, don't tell the Safety Nazis!)

Disc Brake Assembly:
Now it's time to install the mounting brackets and baffle plate.  Use the bolts from the SE assembly.  The ones from the drum assembly are about 1/2" shorter and will not be sufficient.  These are the 4 bolts in rectangular layout across the front of the baffle plate. orient the caliper bracket so that the mounting tabs are pointing up and "forward" with respect to the front of the car.

Install the hubs.  SE or GXE hubs will work here.  Check the bearings in the hub by holding the bearings and spinning it in your hand.. it should be silky smooth.  if you feel any roughness or hear any noises, you should replace the bearings or use the other hub if it's in good condition.  Lube the spindle and hub with plenty of grease. plain ol' axle grease is fine.. it's the thick, brown/blue/green stuff that makes a huge mess.
Install the washer with the tapered end to the inside. The slots in the washer will be vertical. only tighten the hub nut finger tight for now- just until you're sure everything fits.

Install the rotor.  Simply slide the puppy on the wheel studs.

Install the caliper.  I'm assuming you know how to rebuild and/or paint a caliper by now, so I won't go into that explicit of detail.
Use the 17mm bolts that hold the caliper on, and bolt it in from behind the rotor.  Make sure the caliper fits over the rotor correctly.
This is where you will see problems if you got a "mixed" bag of parts from different year Maximas.  If you got the wrong caliper/bracket combination, you will end up either not being able to mount the caliper at all, or the caliper will be so far from the center of the hub that only 1/2 the rotor surface is inside the caliper.   If the latter is your case, you still have hope.  You can remove the caliper mounting plate and drill new holes it to make it fit correctly.  I don't recommend doing this if you have a choice, but that's what I had to do in order to get the job done this weekend.  If the former is the case, wash your hands and take all the parts back to the place you got them and beat the guy with your SE/GXE hybrid strut until he gives you the correct parts.

If everything works up to here, you're home-free!

Tighten the hub nut to correct torque  (tight-as-hell is about the right torque).

Install the brake hoses.  Fairly self-explanatory. 20mm nut on the brake line, and 12mm banjo bolt on the caliper.  remember to install the new copper washers.

Connect parking brake cable.  there is a bracket that bolts to the caliper, then the cable attaches to the caliper also.

Flush all old brake fluid and bleed complete brake system.  According to the Nissan FSM, you should start with the corner closest to the master cylinder (which means front-left wheel).  Work your way to the farthest. (right rear).

Use only DOT3 or DOT 4 fluid.  DO NOT use DOT 5 fluid.  it is a silicone based fluid and is not compatible with DOT 3 or DOT 4 fluid.

Mount your wheels back onto the car.  Have a helper push the brake pedal while you try to turn the wheel- just as an initial safety precaution.  if you can turn the wheel(s) while someone is pushing the brake pedal, you messed up something.  Make sure you connected the hoses and bled the braked correctly, then try again.. if all else fails, call a professional.  DO NOT DRIVE THE CAR! IT IS UNSAFE TO DRIVE. YOU CANNOT STOP.

Check the parking brake for proper operation.  It doesn't have to lock up the rear wheels or be correctly adjusted yet, just as long as it works. (it will self-adjust with time)

Take the car off the jack stands and tighten lug nuts.

Slowly move the car forward or back, and test the brakes.

If everything works okay, go for an EASY test drive.  Do not floor the car and hope everything works at the end of the block. Common sense is a good thing here.

If you did everything correctly, you should now have completed the conversion.  Go home, pick up all your tools, and be proud of yourself. :)