I have the opportunity to play with W2K3 Server thanks to the magic that is MSDN. It's labeled version 5.2 now, so it looks like they monkeyed around with the WXP kernel a bit before making changes.
Anyways, the system ships on 'paranoid' mode. IE is locked down to almost absurd levels (hopefully there's no exploits for it) while no server is installed by default - you have to activate or install them yourself. It went relatively painlessly (I made a backup DC, later I'll move the main home server to the W2K3, probably, as W2K doesn't like that box at the moment).
W2K3: Some thoughts
Moderator: Thanas