Thanks sfisque!
You were right, it's a dual processor issue. For other folks, here are the links to fix the issue:
http://support.microsoft.com/kb/896256 - Link to the MS Support Article
http://download.microsoft.com/downlo...v4-x86-ENU.exe - Direct Link to the Download
Backup your registry, then run the .exe to patch. This fixed it for me on my Macbook Pro/Bootcamp/WinXp.
Cheers,
Hermit