Please elaborate, what Nvidia driver are you installing?
Is it the detonator driver.. if so you have to disable the antivirus software, then windows comes up with the "this driver has not been certified by microsoft" dialogue box, just ignore it, and contine the install.
There are problems with the latest detonator drivers.. I have a Geoforce 2 mx400 and if i run diagnostic tests on my video card it reboots my pc so be carefull.
Hope this helps
--Nick--