1) Go to the card mfg. web site and dl their drivers.
2) Create a restore point.
3) Uninstall your current drivers and reboot.
windows will detect the video card and will want to install drivers - just cancel when prompted.
4) Disable your antivirus (assuming you have one.)
5) Try to install the ATI driver, if it fails again, try to install the mfg drivers and reboot.
If both fail to install, then either there is a hardware problem or other software is interfering; In which case you can do a system restore and be back to where you started.
Other things you can do:
lower the graphics settings for the game.
install the latest directx if you haven't done so.
places to visit:
http://www.tweakxp.com/
http://www.overclock.net/