You didn't say what video card you have, but I'd check card specific forums for game issues, and you might find a different set of drivers that works.
Oh and don't go shutting down system processes, but just make sure your system tray is clean. I swear half the comps I see have close to 10 things running in the tray and wonder why the computer is so slow. If I were to game right now I'd close Firefox and have just 16 processes running, that's including Miranda and the Diskeeper service, so I would try and get it down to around there.