go to downloads section and click on OCing utilities
download coolbits 2.0
then click on it so it'll edit your registry so coolbits is enabled
right click on desktop --> properties --> settings -> advanced --> GeForce 6800GT
one of the tabs on the left will give you the option to OC
click on custom OCing (or something like taht) and then go to 3d (3d is the one that matters, 2d doesn't matter) and click "detect optimal frequency"
400/1100 is the ultra speeds, so if the optimal frequency is near it, then change it to 400/1100 and you'll have ultra speeds
of course, you're gonna have to loop 3dmark05 to test that it won't artifact and download rivatuner to monitor its temperature and see that it doesn't go very high
btw, what brand do you have?