I'd suggest using the correct driver.. that is to say the most appropriate driver for your gpu.. as in the latest Windows Vista driver (they are supposed to work in 7) or the latest Windows 7 driver if available..
By the looks and sounds of it, you don't have the correct driver for your gpu installed.. Also, have you checked device manager to see if there are any problems in there?.... Just because something says it's for Windows 7 doesn't necessarily mean it's the most appropriate driver for your particular hardware..
Curious, what is your gpu?