So Sachs, are you saying that you have tried the Radeon on other motherboards and the video problems move to the new motherboard??? If so, then it's obviously a bad video card.
Have you tested your current computer setup with another video card to see if the problem goes away?? If not, then that should be your next step. If video is good with that card then your Radeon is suspect. If you have the same problems, then you have to look elsewhere for the culprit. BTW, have you checking the 'Troubleshooting' section at ATi to see if others have had the same problems???
Also heat could be at work here too. Is your CPU and/or CPU fan properly seated??? I assume from your system list above that you are not overclocking the Athlon, but if you are then that could be an issue too. Cooling is everything with Athlons.
Not sure this helps, but you asked for input and you got mine anyway!! hehe
Good luck
Hawkeye