Here it is right from the "How To Buy" section of the Microsoft website. From what I can see, it is only being sold with
Ironically enough, the only 64-bit systems I am aware of that come with Windows XP 64-bit are Itanium systems (these are also the only ones advertised on the Microsoft site). Yet in the Windows XP 64-bit demo software section of the site, where you can suposedly sign up to receive demos of 64-bit software being released, the system requirements listed are AMD Athlon 64 or Opteron processors.
Kind of a paradox, isn't it? Windows XP 64-bit is only sold on Itanium based machines, yet the requirements advertised from being apart of the demo program is an AMD machine.