electropretzel: Update your driver version to 275.xx beta like MysterD mentioned above and play on the lowerst resolution and the lowest setting possible. Moreover, close all the unnecessary programs runnning in the background.
Right.
Also, you might wanna run something like FRAPS in the background just to see what kind of Frames you are constantly pushing.
If you're doing fine on a certain setting, than you can change a few things up and down - and see what it gets you.
I'm guessing you'll probably want Field Depth, VSync and SSAO off. Might wanna keep your res' down a bit, too.