Taken from M$ site
Supported processors: AMD Athlon 64, AMD Opteron, Intel Xeon with Intel EM64T support, Intel Pentium 4 with Intel EM64T support
256 MB RAM
1.5 GB available hard-disk space
Super VGA (800x600) or higher resolution video card
CD-ROM or DVD drive
Keyboard and Microsoft Mouse or compatible pointing device
Important: Windows XP Professional x64 Edition cannot be successfully installed on 64-bit Intel Itanium-based systems.