Well, I just finished changing the rear disc brakes on my 03 Astro. Disc brakes are pretty basic to most folks here, but I'm posting for the benefit of those who have never had the pleasure. I didn't think to take photos being this was supposed to be an hour job for both sides, that turned into a nightmare; next time I do work, I take will take photos.
Pad Change:
1: Take a huge C-Clamp, and fit the bottom over the back of the caliper. Fit the top of the clamp over the center of the exposed back of the pad. Tighten the clamp as much as possible by hand, then remove it.
2: Using a 12 mm wrench, loosen, but DO NOT REMOVE the top caliber mounting bolt. Remove the bottom caliber mounting bolt. Note: On the front of late model vans, you'll be using a T-155 Torx Bit. On earlier vans (like my previous 1998) it will be an allen--I forget the size of that one.
Top One:
Bottom One: 
3: Swing the caliper up, and wedge a stick or something under it to hold it up. The GM service manual recommends tying with wire, and that should work too.
4: Using a screwdriver and hammer, tap the brake pads loose from the tops. If you must, gingerly use the screwdriver to pry them loose on each end, but be careful not to damage the rotor--those are over $50 a piece at Advance. If you can't get them off, see below. But trust me, you want to get them loose at this point if at all possible.
5: You've probably already done this. Inspect the rotors for any damage. If they are not smooth, you'll want to replace them or have them lathed. It's worthwhile to find a shop that lathes rotors, as the one near me will do it for $12. (See below if damaged)
6: The new brake pads go in much the same way the old ones came out.
7: Replace caliper, re-install bolt, remember to tighten top bolt. You're done.
Caliper Bracket Removal, Rotor Replacement
This part of the job is not fun. And GM intended it that way. From looking at it, you'll note that it seems straightforward The two bolts you're looking for are the big ones behind the rotor. They are torqued to 148 lbs. And the top one is a !%!@% to remove.
1: Spray the bolts with some penetrating oil to make your life easier (WD-40, PB, etc). Edit: First use a blowtorch on the bolt head, then spray it with the PB Blaster. If you have a really good impact wrench, try it on the bottom one first... Repeat these steps a couple more times. Here are the bolts I'm talking about:
Top One:
Bottom One:
2: Using an 18 mm socket and an impact wrench, if you have one, remove the bottom bolt holding the bracket. The first time around on this job my compressor was a pancake style unit, this didn't work out too well for me. If you find yourself in this boat, use a breaker bar and fit a 1.5 inch steel pipe over the back end. With the right amount of leverage it'll come off. Use a long enough pipe and you can just step on it from the back of the van.
3: Using an 18 mm wrench, preferably with a 6 point back instead of a 12, remove the top bolt holding the bracket. You'll end up hitting it with a hammer to get the bolt to move. Alternatively, fit a shorter length of 2 inch steel pipe over the wrench for some leverage. Do not use a socket and rachet to remove this bolt. I tried that with a 3/8" drive socket and rachet, and the top bolt backed the rachet into a bracket holding the leaf springs to the axle. A universal won't work either. There's too much torque and locking compound on those bolts... Edit: Don't be afraid to re-apply the blowtorch and PB Blaster a couple times when you hit sticking points.
Note: Don't just let the whole assembly drop as you remove the bracket. You could damage the brake line to the caliber if you do. The GM manual says to tie it to something, but I find that putting the caliper assembly on the leaf spring works just as well...
4. Pull the old rotor off and replace it. Note, you may need to hit it front and back repeatedly with a mallet--it may be stuck. Also, others have indicated that a blowtorch applied to the base of the rotor, where it mounts to the hub, can be helpful here as well...
Old Rotor Off:
New Rotor On: 
4: Replace the bracket the same way you removed it. If you feel strongly that you need to torque the bolts holding the bracket to 148 lbs, let me know how that works out for you with the top one ](*,)
