Well, for what it is worth you cant run a p4 on a 250 watt ps either. Kinda suprised at you, the fact that you need a 300 watt+ power supply is a well known issue. I don't doubt you have assembled systems before, however I can't beleive you actually tried to just swap motherboards and processors and expected it to boot up without issues. This is a tell tale sign of your expertise. Sure, you have spent a lot of time with this system and you are thinking that it is the worst POS you ever seen, but know face the facts. You, yourself caused half this heartache by first trying to take a shortcut, and second trying to eek by with an underrated power supply. for all you know right now, all your troubles could have been caused by the PS, and for this you blame AMD? They come right out and tell you that you need an approved power supply. Then, discounting this as the possible problem, you install via busmaster drivers when even VIA themselves ( read there website) recommends you use microsoft default drivers. Then, and only then you decide to sit down and read the manual. Let me explain, 3dmark puts a strain on your system, expecailly the video card. Your video card uses quite a bit of power. The poor thing was doing all it could do just to power your devices and cpu. As soon as you tried to run 3dapps and the video card needed a little more juice, yeah it konked out on ya. Unfortuantly now, after so many attempts at different drivers and all, your windows reg is totally screwed. Anything other than a complete format and reinstall after you get the new power supply will be just asking for trouble. I suggest this, get the new power supply, reformat and install just as i said. If the problems continue then RMA the board and be done with it. If, everything works as it should, then you should take a good look in the mirror to see the source of your problems.
Now I know why so many intel users have trouble with AMD systems.
A little bit of knowledge is a dangerous thing!