Unattended Windows installations still need an administrative account; credentials can be left in one of the following files (if not cleaned up):
C:\Unattend.xmlC:\Windows\Panther\Unattend.xmlC:\Windows\Panther\Unattend\Unattend.xmlC:\Windows\system32\sysprep.infC:\Windows\system32\sysprep\sysprep.xml
Look for the <Credentials/> block.