Ok, some things you might want to check. I had the same problem with my new
PC. When I got my
PC, it had a driver installed. When I updated windows, that too had a driver update. I am taking a guess that these two do not play well with each other. If you just have an Nvidia Graphics card then you shouldn't have a problem getting into the registry after uninstalling your current driver and delete ALL the registry keys that have Nvidia included in the name. This will give you a clean platform to install the new 163.69 driver off the web. If you have a Nvidia Chipset, BE CAREFUL WHAT YOU DELETE.
After I did this, the new 163.69 driver cranked my ranking back up to where 5.0 like it was when I first purchased the computer. It was at a 4.7 with a 8500GT.
Also, I am sure you know this already, but Vista comes default with a balanced power option. This will screw with your graphics big time. You will need to crank the power to the High Performance setting located @ Control Panel>>>Power Options.