I've known about this CD image (link is a download) for a while and have used it successfully on many customers computers. Here is the website associated with it with more details and all sorts of helpful information. Bottom line, it's a bootable CD that will allow you to reset or change Windows user passwords.
The CD is usually my last resort. First thing I like to try is logging on to the administrator account. Most computers have an administrator account that has never been logged into. This is especially true with OEM (Dell, Gateway, etc.) computers. Not only have these accounts never been used, they've also never been set up, and more importantly they've never been password protected.
One way to get to this account is boot the computer in safe mode. This can be achieved by holding F8 during bootup. Safe mode will bring you to the friendly Windows Welcome screen showing, not only accounts on that computer, but the administrator account. If safe mode isn't your thing just hold ctrl+alt+delete at the welcome screen until the traditional windows login prompt comes up. The administrator account will be accessible simply by typing 'administrator' into the user name and leave the password blank. No welcome screen? Just go down to the start menu and log off. If the computer only has one user account Windows will log onto that account without showing the welcome screen. In most cases that will get you into the system without having to remove others passwords.