Today at work I had another occasion to use NT Password which is “a utility to (re)set the password of any user that has a valid (local) account on your NT system, by modifying the crypted password in the registrys SAM file.”
This is a handy tool to keep in your arsenal for Windows NT/2000/XP work. It's based on a small Linux distribution and fits on a boot floppy or CD. If the administrator's password has been forgotten, you can use this to reset it. Of course, this can also be used for nefarious purposes. Fortunately this is a brute-force password “reset” tool, not a “recovery” tool. If you use it to break into someone else's system, the fact that the password has changed will be noticeable.
This also is a good reminder why having physical security to your computers and servers is so important. If someone can walk up to a system and boot to a different OS, there really isn't a limit to what they can do.