We've had one report that the Windows Genuine Validation tool wouldn't work
right on a 64 bit machine.
I'm skeptical about this report--I've downloaded Microsoft Antispyware on
several 64 bit machines, but running 32 bit XP. I've got a 64 bit XP
install, but alas, no drivers for the only available wireless nic on the
box.
So--if you'll tell us whether it passes WGA, I'd be glad to say "sure, go
ahead" on your install!