I re-read your post to see if I missed anything or did something stupid. I saw that you are using a Radeon card. The only thing I can think of being the problem that is ATI-specific is Catalyst Control Center. I know that many versions of CCC are notorious for interfering with games to the point of making them unplayable. It is why I won't use ATI/AMD graphics cards any more. However, I am grasping at straws, at this point.
