From: "Frank Haber" 

For a self-serving white paper that nevertheless may tell you some of what you want:

http://www.microsoft.com/technet/itsolutions/msit/operations/mscom64bitarchi.ms
px

Driver support is a problem.  My bleeding edge buddies have retired the HDs
that contain desktop 64 bit XP installs, for the mo.  Server-side, 64
sounds priceless if you need it.

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