>No, my question is more along the lines of is there any reason hardware-wise that I cannot uninstall 32 & reinstall 64? How do I know it will work?
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>>If you mean do an upgrade you can't do an upgrade install from any 32bit windows to 64bit as far as I know. Plus I would think it would be quite a pain in the neck because aren't all the drivers and such going to be different?
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>>>I have WinXP 32 Bit on my laptop. Can I install WinXP 64 bit?

I agree with William, I think you'd be better served by Windows 7 64-bit. XP64 was never widely used, you'll probably encounter driver issues which will never be resolved because XP is considered obsolete by MS.

MS offers a Windows 7 Upgrade Advisor: http://www.microsoft.com/windows/windows-7/get/upgrade-advisor.aspx