i am a ati video card user, and i have seen many weird video problems. first, unistall the video card on the device manager, dont restart. then go to the ati folder where the drivers are and delete it. then reinstall the new catalyst drivers. note that you will need the lastest direct x for teh catalyst driver. once the video card is reinstalled, check if the problem persist, then you ahve to check the bios settings for agp. if you have a 64 mb memory in the video card then configure the agp to 64 mb minimum aperture.
some thimes it s depend the game, and sometimes is any other driver that is messing up the game, so if the problem persist try to check all devices if they are working properly