XP as Domain Controller ?
Well... Not really. But here is a nice tidbit:
1) Create a share called SYSVOL on an XP box
2) Try to unshare the directory you shared as SYSVOL.
3) You will get a nice warning stating:
"This share is required for the machine to act properly as a domain controller. Removing it will cause a loss of functionality on all clients that this domain controller serves. Are you sure you wish to stop sharing SYSVOL?"
Here is a screenshot:
But do not worry - unsharing SYSVOL on XP will not break your AD. My guess is that this is a direct result of code parts reuse between various versions of Microsoft operating systems, yet it's funny to see XP claiming to be a DC ;)