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Major contributor!
Well, it may very well be free. Better yet, it may be free from none other than Microsoft. Granted, you gotta won XP to do it, but hey, if you have a 64-bit proc, you might want to give it a try on release.
http://news.zdnet.com/2100-3513_22-5481660.html
Those who own a 32-bit version of Windows XP Professional or Windows Server 2003 will be able to exchange it for a license for the 64-bit edition, Microsoft has said.
http://news.zdnet.com/2100-3513_22-5481660.html