My long in the tooth ASUS K8VSE AMD3700 64bit ran really fast on RCWin7. It was definitely faster. I had no problems finding drivers for the AMD X800 256 AGP Pro Video card and this was with just 2.5G's of Ram.
I may run WIn7 on separate hard drive as I have 3 500G hard drives with one basically doing nothing, but I would have to pay twice if the machine breaks down and then have to rebuild, so I just may wait till I build a new machine.
I have Vista Sp1 64bit that I purchased but heard so much negative stuff about it I never installed it. I may install it on this machine, since I have it, oh well.