You cannot use WinPE for this. You have to restart Windows 2003 in Directory Service Restore Mode.
Note: At startup, press F8 and choose Directory Service Restore Mode. It disables Active Directory. When the login screen appears, log on as Local Administrator.
Local admin needs the Directory Service Restore Mode password. If you don't have it anywhere written down, changes are that it's "password" or something similar. If you don't have the DSRM password, or can't hack it, you're in trouble.
