To sum up !
1). (Skip this if already uninstalled)
Uninstall your current ATI display driver. Do this by going into your control panel and running add\remove programs.
Choose yes when it asks if you would like to uninstall.
Choose no when it asks to reboot.
2). Delete the Ati folder under C:\.
Remove any leftovers with drivercleaner. Do this in any circumstance to get rid of any ati driver related files on your system.
3). Reboot your computer. Windows should now load with default VGA drivers.(if not go to 4, if yes got to 5)
4). Go to Control Panel\System\hardware\devices. Look for display adapter and uninstall. -> reboot.
If windows still cant find it pop in your xp cd and choose update driver in the hardware devices\display adapter, choose search and check the search cdrom option(if your connected to internett you could also try windows update). Let it finish -> reboot.
5). Install the new ati drivers, -> reboot