Its a bad contact...You need to get yourself down to your nearest computer shop and pick up some thermal paste. Take your fan and heat sink off and put a blob on the GPU.
Stick it back on and you'll be back down to 35'C before you can say: "never buy XFX"
Hah, I had a 6600GT and it idled at 60 Celsius, and went up to 98 Celsius. I think you're okay with a 65 Celsius load temperature . Unless, of course, the 6800GS isn't supposed to get that hot, I don't know. My 7800GT gets up to around 68 Celsius under load.
I don't know if that's to hot or not. I used to run an ATI Radeon 9250 at 78 Celsius at one time, so I think you're OK. But my current card never gets any higher then 45C, and that's under a HUGE load. It's all thanks to the Kingwin Super-Heatpipe VGA cooler! Thing's a beast!