@valente500: Before starting a game, run nvidia-settings once. It will "initialize" the card with proper settings. I don't know why the driver from nvidia doesn't correctly "zap" the card at startup but the settings dialog does. Also, on my computer, shutting down desktop composition made all the difference (all games ran at half speed with desktop composition on) - this in Kubuntu 10.04 with a 260GTX card.
