Re: GeForce 6800 - Can't Install New Driver
Have you tried without the clean install option?
If you want a clean install, it may be slightly more complicated:
Nvidia changed their installer around the 250s serie and i'm not sure how well it works to ask it to clean the older driver. Try to manually remove the older driver (control panel->remove software->nvidia driver), reboot, prevent windows from installing any driver at reboot detection and then run the driver.
As the universe is curved, there cannot be a straight answer...