Forgot the Administrator's Password?

Ok, so you say you forgot your Windows administrator's password, huh? Oh well, it doesn't really matter if you did or you just say you did. The fact is that you need to gain access to a computer and you cannot "remember" the administrator's password.
How can you get out of this situation without formatting and re-installing the operating system?
Well, you can always try to remember the login password, or if that doesn't work (you wouldn't be sitting here reading my crap if you did remember, would you?) you can restore a backed up System State (in W2K DC) or a ERD (in NT 4.0) in which you do remember the password. The problem with doing so is that you'll probably lose all of the recently add users and groups, and all the changed passwords for all of your users since the last backup was made.