The only thing we know for sure up till now is that anyone still can install Windows Vista or 7 or even 8 on an AGP + nForce 3 + multi-core motherboard but only if all cores are disabled down to one.
I am using my Gigabyte HD 4650 AGP with Windows 8 at the moment and the acceleration is enabled though I can't play any new games because my system works with only one core enabled. It is a tough problem indeed. You must choose graphics acceleration or multi-core support yet both of them no way.
If we found the solution to this, I would say ancient, issue we are probably going to win a Nobel price.
P.S: By the way, cdawall's beta XP64 nForce drivers didn't work for me on Win 7 environment but I'm not sure if I did the installation correctly. I was too confused that day.