OK don't panic!!!
This is of course not an editing question blah blah blah - go to the official forums at BIS.
HOWEVER, I hate to see someone in trouble. I upgraded my videocard to a radeon 9700 and had the problem that all the ground textures flicker badly. This problem and others was solved by getting an official radeon patch of the website.
If that doesn't work and you've got XP then there's this weird video type thing (technical) that microsoft have stopped including in their packages that is required for most modern games to work effectively.
Sorry for the lack of technical expertise. best go to the official forums of BIS and RADEON. My main aim hjere was to tell you it CAN be fixed as i had a similar problem.
Good luck and RELAAAAAAAAAAAAAXXXXXXXX!!!