I found a fix for my system with a 7800 series video card and a dual core amd x2.
It was a link on a nVidia forum. It worked for me; I had to make a change in my registry I guess. I don't completely understand what it did but my game went form unplayable to working perfectly.
http://forums.nvidia.com/index.php?showtop...484entry63484
nVidia Forum with link
Hope this helps, read the post in the forum and the linked page for directions.