Well... I got them to copy by cleaning the discs really well and using a different, newer burner...
corpse: I tried what you suggested but I really don't trust NoCD cracks for a game this old... on the two occasions I've tried, they've skipped videos and generally acted strange, so I decided I was better off just doing a straight rip again. Thanks though!
So I'm now the owner of a legal backup copy and can play without worrying about destroying my discs... I'm happy!
Now to try those hi-res patches I've read about!