MarineCorps
Explosion!
Do your homework before you plunk down the $$ for Vista Ultimate, 'cause there's really no reason at all to get it instead of Home Premium.
Home Premium (64 bit) is very reasonably priced at $112 - which is $40 cheaper than XP Pro (32bit).
Unless you are getting Ultimate edition for free.

oh! i had heard that only Ultimate supported 64 bit. i guess i heard wrong. whats the main differences of Vista Home x64 and Vista Ultimate x64??
Combining all the features of the Home Premium and Enterprise editions, plus the "Ultimate Extras", Windows Vista Ultimate has features such as business quality encryption as well as Windows Media Center. Ultimate supports up to two physical CPUs[6] and 128+ GB of memory (64-bit version). Mainstream support for Ultimate ends on April 10, 2012; extended support ends on April 11, 2017. There is also an upgrade variant of Windows Vista Ultimate available, Windows Vista Ultimate Upgrade Limited Numbered Signature Edition. This is a limited, numbered edition of Windows Vista Ultimate that features Bill Gates' signature on the front of the packaging along with its unique number; only 20,000 copies of this edition will be produced.