I had to do this once to change the password of a machine's account (the machine's previous user had left the company). Of course, I used an Ubuntu live DVD to

I had to do this once to change the password of a machine's account (the machine's previous user had left the company). Of course, I used an Ubuntu live DVD to do the file renaming. It's the cleanest method, since it allows you to use Window's own routines to change the password, instead of an external program which might miss updating something. But the interesting part of this post is the trick to do the file renaming without having to boot from any external media. This bypasses any security preventing the use of external media. Even if a user has access only to the keyboard, mouse, and power button (or can cut the power by pulling the cable), he can use this trick to do the file renaming and gain local admin access.