Other than a clean Windows install (yuck!) the only other thing I can think to try is to uninstall the display drivers and then try running it with only the display driver with no SMARTGART or control panel. That's the simplest possible software environment. Just the display driver and the GART driver and nothing else.
1) Uninstall your display drivers using the
ATI uninstall utility.
2) Reboot and then install the latest hyperions just to be sure your GART driver is still okay.
3) Go to
www.ati.com and download the version which includes only the display driver. It's the "Low Speed (Dial-up)" one which says "Display Driver". That version doesn't include the control panel or SMARTGART. It's the simplest driver you can use. Install that driver.
If it doesn't work then you could try the older display driver only versions at
www.ati.com under "Previous Drivers and Software".