Windows admin interview questions (includes Vista)
Demote the server using dcpromo /forceremoval, then remove the metadata from Active directory using ndtsutil. There is no way to get user passwords from AD that I am aware of, but you should still be able to change them.
Another way out too
Restart the DC is DSRM mode
a. Locate the following registry subkey:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\ProductOptions
b. In the right-pane, double-click ProductType.
c. Type ServerNT in the Value data box, and then click OK.
Restart the server in normal mode
its a member server now but AD entries are still there. Promote teh server to a fake domain say ABC.com and then remove gracefully using DCpromo. Else after restart you can also use ntdsutil to do metadata as told in teh earlier post