Your best bet is to try and clean it, or take it to a nearby computer store that can restore scratched discs.
Failing that, you've got two options:
1. Download the game off of a torrent site somewhere and emulate it on your PC, which will be difficult to do without a upper mid-range to high range computer.
2. Go to a nearby video game rental store, rent the game in question, and switch the discs.
Either option is potentially illegal and could easily land you in trouble, so I really suggest getting the disc repaired first.