http://www.techspot.com/news/33310-m...-be-64bit.html
"We’ve been able to make the switch to 64-bit operating systems for a while now, but driver compatibility issues and the mere fact that there wasn’t a lot of need for it have held up widespread adoption. Things have been changing rapidly in the past year, though, according to Microsoft, with about 25 percent of all Vista installations in 2008 opting for a 64-bit setup."
I'm on 32-bit XP, but rctneil has a point... especially for the future...