Rancid, id make sure youve installed all of the updates available for the game (go to the raven website) and all of the latest drivers installed for your video and sound card. You could try running the game on lower graphics settings.
Its usually one or a combination of the above, either that or youve got a bad CD with files missing, get it replaced. If your using a pirate version of the game it could be anything.
If the game runs totally fine up until that point it sounds most likely that the game installation is bad, your best bet is to reinstall the game, it should give you the option to backup your saved games.