Sorry to disagree with you but 64 bits OS became verry popular with AMD 64 CPU, faster and cooler than P IV equivalents. I've installed my first XP64 on an 3200+\2GB DDR machine more than 1 year ago. At that time there was a lack of drivers, but OS was OK IMHO.
All Vista releases will be 32 and 64 bits.
LE:
http://www.microsoft.com/windowsvist...s/default.mspx
And by the way, microsoft's windows is the one coming in two versions, 32 and 64. Linux for example have support for 64 bits architecture for 2 years now.