find some Displex, if you google it it should come up. Its meant to remove scrathes from mobile phone displays and comes in a pack with some paste and cloth.
The trick is to use it and be paitent, take your time, rub it in gently in circle motions (as the pack advises) and eventually you'll polish out the scratches.
I wouldn't expect miracles though, if its badly marked/scratched the best you can hope for is to make them less obvious.