On a model 1? It's very easy, especially if you've ever done work inside a system before. (Although I assume it's very similar, a model 2 might be different.)
Tools needed:
- phillips head screwdriver
- your fingers
Steps:
- 5 screws hold the case together from the bottom
- 2 more screws hold the disk drive in place.
- disconnect the ribbon cable
- carefully lift the drive out
Flip if upside down and you'll have access to the belt
Good luck!
If you don't mind me asking, where did you buy your replacement belt from?