ExtremeTech puts 64 bit Windows XP Professional through its paces on dual core processors here. There are still many more tests to do but here are the initial findings:

Driver issues aside, Windows XP Professional x64 Edition seems to be stable and solid operating system, and we can cautiously recommend it if you’re willing to live in a dual-boot environment and are willing to manage your expectations when it comes to driver support. We’re really encouraged by the minimal performance losses and encouraged by the potential gains of 64-bit applications.

[Check it out]

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