First things first -- Don't drop it on your head! Last thing that'll go through your mind will be your eyeballs!
Removing a tranny isn't that tough. If the exhaust goes under it, you'll need to drop the exhaust, if it goes over it (not likely) then you can leave it.
You'll want to take the driveshafts off first, then remove the transfercase. To drop the transfercase, use a hydraulic floor jack, lift it up under the transfercase, using a 4x4 if you have to extend the reach of the jack. Strap the transfercase to the jack using a tiedown strap, or something similar so it can't fall off the top of the jack, then carefully lower it down.
Be warned, when you split them apart, you're gonna get ATF puking out of the back of the transmission, and probally some gear lube from the transfercase too.
After you've got the transfercase down, then carefully slide it off the jack, and onto a creeper or something, so you can roll it out from under the truck.
Now that the t-case is out of the way, its time to tackle the transmission.
First, you'll need to jack the tranny up by the pan, and remove the mount the adapter is bolted to, and slide it out of the way, remove the TV cable / kickdown cable (depending on your tranny) any vaccum lines, the shift linkage, any anything else that may be attached to it. We want to drop the tranny, not test the tensile strength of various cables, lol
Once you've got everything unhooked, then remove the flexplate inspection plate, using a 9/16 socket on an impact gun with an extension, take out the three bolts that hold the torque converter to the transmission (my bolts there were 15mm for some reason, but most I've seen have been 9/16) If you don't have an impact gun, you'll need to find some way to hold the flexplate so the engine won't rotate, while you remove them with a breaker bar.
Next up will be the bellhousing bolts. They are 9/16s most of the time, and usually come out fairly easily. There are two you must get from the top of the engine, and two to come out from either side. The top and driver's side are easy to get at, so save them for last, so you don't kill something while trying to get the two from the passenger side out
If you've got manifolds, it isn't quite so bad, but with headers, its a real pain in the butt.
After you've got all of those bolts out, and you are 100% sure that everything is dissconnected from the transmission, find yourself an axle stand, with a peice of 2x4 to set up under the oil pan. When you drop the transmission out and back, the back of the engine will want to drop, and if you let it, you'll wreck your engine mounts. After you have got the stand setup, then very carefully pull the transmission back, off the pins on the bellhousing, and lower it down. Take your time, and never put yourself into a postion that the transmission could fall on you. While you are letting it down, watch to make sure that you notice the TV cable tightening up cause you forgot to unhook it, before you wreck it! lol
Once the tranny is down, again, transfer it over to a creeper, and roll it out from under the truck, and voila, you have your tranny out. Installation is the reverse of removal, and typicall a bit more challenging, as you gotta line stuff up for bolting things together, and sometimes that can be a real pain in the butt!
Good luck, and if in doubt, ask questions!
EDIT:
Just a note I remembered for re-installation:
Before you try and jack the transmission up, you need to make sure that you have the torque converter seated all the way onto the input shaft. Usually there are three "steps" to get it all the way on. To make it go the next step, you gotta rotate, and push at the same time. You'll know you are all the way in if you have got a good 1/2" between the flexplate and the torque converter with the bellhousing all the way up against the back of the engine.
If you force it on by tightening the bolts, you risk breaking your flexplate, torque converter, and more lethally, your transmission's hydraulic pump housing.
)--that will lead to chattering and might make the clutch "drag",and not release all the way..not many of us can bench press a SM465 and stab it right in on the first try,and not let it "hang" while trying to get a bolt started.. 
