You don't need to re-install Windows NT/2k/XP/Vista if you forgot your admin password.

Offline NT password and registry editor is a freeware utility to reset / restore the password of any user that has a valid (local) account on your Windows NT/2k/XP/Vista etc system.

You do not need to know the old password to set a new one. It works offline, that is, you have to shutdown your computer and boot off a floppydisk or CD or another system.

Will detect and offer to unlock locked or disabled out user accounts!
There is also a registry editor and other registry utilities that works under linux/unix, and can be used for other things than password editing.