Here's the standard reply:
Make sure you change your display adapter (in the advanced setting of the display properties) to "Standard PCI VGA Adapter", then reboot, then install the new drivers, then reboot.
Since that's probably what you did already, You might want to consider doing some registry hunting after you change the adapter to see if you have conflicting keys. I had a problem once where the system crashed in the middle of the drive update and I had to manually remove everything related to the video card from my registry before I could get a clean driver install.
Hope this helps.
(of course, as I look back at this post I realize how little content there actually is, sorry)