Go to www.guru3d.com
, they have programs that will completely remove drivers for ATI or nvidia. Not sure if they have one program that will do both companies or one for each. Think it's called like "detonator driver remover" for ATI. But yeah going into safemode and removing the files using that program is the best way to do it.
I know I love my 6600GT thus far...let me know what you think of yours
I OC'd it the first day. Got 565/999 (just under a GHz damnit!)
and that raised my 3dmark03 from 7555 to 8200, I'm thinkin if I do 550 it will probably withstand 1ghz on the memory, but it's the first day so I didn't really give it time to warm up and burn in haha