I'd suggest you stick with 32 bit XP and 32 Vista. 64 bit starts MS's drive for signed drivers (The very reason so many drivers are lacking) which is how MS plans to piggyback DRM (Digital Rights Management) onto your PC to make the RIAA and MPAA happy. I have friends even at MS that are not happy about this plan.
-S
PS. I have both running on a couple systems and I can't tell the difference between 32 bit and 64 bit anyway. Both are smooth. Its probably lack of apps in 64 bit which is why I don't notice much.
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