if your using windows 7, Open Programs and Features by clicking the Start button , clicking Control Panel, clicking Programs, and then clicking Programs and Features. Then select Nvidia driver, uninstall and remove the driver and all of it's components. and you should be set.
Then download and install the latest driver from
http://www.nvidia.com/Download/index.aspx?lang=en-us
if you still keep getting errors with the drivers, that means you have to completely remove everything. In that case, use
http://download.cnet.com/Advanced-Uninstaller-Pro/3000-2096_4-10069986.html and remove every single associated files. Its easy to use but if your having trouble let us know.