Yeah, if it's a 64-bit CPU, Windows XP 64-bit should work. But again, let me reinforce the downside to the X64:
-64 bit kernel cannot use 32 bit drivers, obviously, so hardware support is slight at best
-Practically have to build your system around what hardware it supports from either natively or 3rd party sources.
-Most programs won't run much faster than most people would like at this time
-Completely 64 bit programs are awhile coming - very few available at this time
-Microsoft seems more interested in Vista at the moment
-Performs poorly with 64 bit AMD processors, and older P4 64 bit CPUs.
-Pentium D CPU seems to work best (more expensive)
-Very poor driver support/availability
-Some 32bit programs simply will not run - especially antivirus programs
-Many web related bugs and incompatibilities. Active X, for example, won't work. Possiblr conflicts with Flash or Java as well.