I don’t want to repeat the whole article, just the essence of it. Fire up your windows XP CD, boot from it, select Repair and let the repair process do its workings. Reboot when its finished and when you see the Installing Devices progress bar, press SHIFT + F10.

A console appears, enter nusrmgr.cpl and you have graphical access to your user accounts. You can change or remove passwords for all accounts and or type control userpasswords2 and login without being asked for a password. You will have to continue with the repair process though, it won’t work otherwise.

A pretty handy solution, the article also gives tips on creating a password rescue disk.

Another solution that may be viable in some situations is the following. If you have a second administrator account, you can simply sign in to that account to change all other user account passwords from with the Windows interface.

Administrators need to open User Accounts in the Control Panel. There on the Users tab they can reset the password of any local user account. Once the password has been reset enter a new password and confirmation password and click ok to set it. The user from that moment on has to use this password to log in.

Additional information about this procedure, and how to change a user password with limited rights, are available on this Microsoft documentation site for the Windows XP operating system.