As above. Clean it thoroughly first to decrease chances of failure, but modern PC drives are pretty good at reading even ruined discs.
A good tip - Use toothpaste to clean it. The whitening kind, without any bits in it. Smear the disc in it, then leave it for 10 minutes. Rinse it off with warm water and wipe it clean. It fills in most of the surface scratches and makes it incredibly clean. Really deep scratches are difficult though.