The SP2 web site indicates the same service pack can also be installed on Windows Server 2003
http://www.microsoft.com/technet/windowsserver /sp2.mspx
This is a good sign because MS are unlikely to release a SP that causes problems on their Windows server product.
Having said that, Windows Server 2003 is NOT the same as XP x64 so it could work on the server product but cause problems on XP x64.
There are unlikely to be many people here running XP x64 so why not ask on a more specific forum.
Here is an XP x64 forum on the Microsoft web site
http://www.microsoft.com/windowsxp/expertzone/ newsgroups/reader.mspx?dg=microsoft.public.win dows.64bit.general