Il me semble que le processeur doit être 64 bits et supporter les instructions de paravirtualisation Intel VT et Amd Pacifica.
http://citrix.com/English/ps2/products/feature.asp?contentID=1297950XenServer Host:
64-bit x86 server-class system
CPU: 1.5 GHz minimum, 2 GHz or faster multi-core recommended
Intel VT or AMD-V required for support of Windows guests
Matching CPU family and stepping required for all systems in Enterprise Edition resource pool
1GB to 128GB physical memory
100Mb/s or faster NIC
Local or Fibre Channel boot disk with 16GB of space minimum, 60GB or more recommended