Which operating system for CFX is the best?

Dr. Bian

Several DELL workstations (P4 3.4GHz, 2-4G RAM) are supposed to buy for a small cluster. The remain question is operating system:

WinXP32: Popular, compatible to any existing hardware, but no 64-bit benefit. Need to update OS later for 64-bit CFX.

WinXP64: Still in Windows family, more familiar, but may have compatible problem. No 64-bit CFX now, but will be in CFX-11.

WinClusterServer2003: It is 64-bit OS, no official release yet.

Red Hat Enterprise Linux WS v4 for EM64T 64bit system: Take advantage of 64-bit computing with existing CFX, address more RAM. Faster speed is reported. But less familar than Windows, do not know the compatibility with network and other Windows PCs

Any suggestion and comment here? Thanks