Well. One of the issues is not that it doesn't run. It won't run with the G3 Sonnet upgrade card in it. It seems to run fine, but it freezes and i think it's preventing air from getting to the G3 L2 upgrade card. Or the power draw of both the G3 and the ATI is an issue.

I have heard of other issues with G3 upgrade cards and ATI video cards in te 6xxx series. I think it's a firmware bug someone figured out with the power macs.

I see it on the 6400 Zone a lot. So I may be running into issues the same ones they describe