Package chntpw: Information

This little program will enable you to view some information and change user
passwords in a Windows NT SAM userdatabase file (NT/2k/XP/Vista etc system).

You do not need to know the old passwords. However, you need to get at the file
some way or another yourself. In addition it contains a simple registry editor
with full write support, and hex-editor which enables you to fiddle around with
bits&bytes in the file as you wish yourself.