This could very easily just be your video card drivers. I see you have vista which I have as well and for a while before I installed this latest round of drivers for my card I would have similiar issues (mine are Nvidia drivers) heck I couldn't even play some games at all on vista because of the video drivers however now I can without issue. One exception I have recently noticed is that I can still have issues and get the message you get if I allow vista to go into sleep mode or what ever it goes into when you leave it for an hour or so. When I try to game after that I usually have issues. A shut down and restart clear it and then no more issues. But vista definately still has sleep issues.