Hello,
I've recently done a similar thing, I switched from 32 Bit XP to 64 bit Windows 7 and am running Maya 2008.
I just checked my old 8.5 installation disc though and there's a folder on it called win-amd64 so you should be ok. I can't speak for XP 32 but I haven't had any issues with Windows 7 and Maya 64 bit. Hope that helps!
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