Nope, there is no special "MIL-SPEC" version of Windows.
Everything that the U.S.Army currently buys for workstation use is WinXP Pro.
Absolutely NO WinXP Home or Media Center Edition.
Of coarse, there are alot of commercial vendor add-ons for aditional security and remote access options, and it is kept locked down to the point that the average user can't install any kind of hardware or software, but it's just WinXP Pro.
Currently, ALL individual user Logon access to individual workstations is handled thru the CAC card.
The "Common Access Card" or CAC is a "smart" ID card with an imbedded computer chip that stores encrypted user info/passwords, and security certificates.
CptA