I get this too, but changing the resolution or disabling/enabling realtime shadows usually temporarily fixes it until the next time you launch the game.
This problem seems to be more prevalent on Vista than XP, of course these games were never made or updated to be compatible with Vista.
A gripe I have though is I can not choose 1280 x 1024 resolution or higher, the max it goes up to is 1280 x 920, possibly not even that.