I had just that problem with a MSI FX5600 not two days old. I tried /everything/. Uninstalling, running destroyer to sweep clean reinstalling about three different driver sets even Omega's nothing seemed to work. Not just AH but all my 3d apps. So...btw I even did a fresh format of the HD and reinstall using win98SE, Win2k, WinXP AND Server 2003. Nothing worked with the card.
So, I did a search for the latest Beta drivers which every says not to touch because they're buggy? Well at least for my Fx5600 card they cured all my ills the first time around. I've had zero errors not even a trace of an artifact when OC'ing the card. They work flawlessly. At least for me.
Win2k with all the updates.
1.8Ghz Intel on a Ecs motherboard.
728meg of ram
MSI Fx5600