Frank: I'm sorry but I cannot tell as I have never used the 64bit version of Windows XP.
However I'm considering buying it just to have an option to not use vista when I'm going for a new computer with more than 3GB someday.

However I did a quick google search and found this article (more than 3 years old) about WinXP Pro 64:
http://www.zdnet.de/enterprise/os/0,39023494,39132549,00.htm

Here is another article (also 3 years old):
http://www.pcwelt.de/start/software_os/w..._moeglich_sein/