Not too long ago Windows XP was preferred over Vista for 2008 Beijing Olympics due to concerns over the stability and maturity of the new platform and now as a final blow Windows users worldwide have the option to Officially Downgrade to WIndows XP.
Apparently it is cleared in the license terms (as if we read it) that any one using OEM versions of Vista Business and Ultimate Editions can downgraded to XP without additional cost.
From OnlyGizmos