Okay folks, in this thread you can discuss all suggestions given by ATI support. Which helped you, improved performance or image quality. Or even which of the options supplied did not do any good or were complete nonsense...

I just noticed that my Radeon 8500 was SHARING IRQ 11 with 3 (!) other devices which was causing lockups in WinXP. First of all I was clueless on what to do but then I disabled my COM ports in BIOS which were not in use as well as my USB port and tada -> Radeon was only sharing IRQ with the Audiyg firewire controller (since I have no use for that I also disabled this device via Device Manager). As of now no lockups :smile)

Both Windows 2000 and Windows XP manage IRQ resources, so you will most often see
Microsoft ACPI-Compliant Systen on IRQ 9, followed by all non-legacy devices sharing IRQ 11. Disabling unused devices is definately the way to go.