Windows 2000 proffessional Locked

One of my friend brought laptop from our Delhi office.Our office in Mumbai have simple workgroup connectivity as our Delhi office has Domain based connectivity.
The friend from delhi office wanted to copy some presentations from our local network(MUMBAI)to his laptop which has windows 2000 proffessional .
thus he simply make his machine join our MUMBAI work group instead of Delhi domain using network identification wizard.after that his laptop asked for rebbot
After reboot his laptop is not accepting his own login name and password and he doesnot know the administator password for his machine
he is not able to login to his machine
Plz suggest a way out from this without losing DATA