chntpw :

move to the SAM folder:

cd /media/disk/WINDOWS/system32/config/

show users:

chntpw -l SAM

reset password / unlock user

chntpw -l SAM

cd
umount /media/disk

links:
http://forum.s-t-d.org/viewtopic.php?id=2026
http://linuxbasement.com/content/changing-nt-passwords-with-linux-and-chntpw
http://www.mydigitallife.info/2009/02/03/reset-and-change-windows-nt2000-administrator-or-user-password-with-chntpw-in-linux/