Forgot your password Windows XP or Vista?
No problem, there is a free program that suits you. It's called ophcrack and you can download the following link.

Operation is simple as downloading an ISO image that you burn to a CD, then restart your computer with the CD inside.
As the program is a Linux Live CD auto start and its cargo shows a screen with the list of Windows users identified by the program. From here you can select the desired user and click on "Launch" to locate the password.
The duration depends on the drafting of the password length to locate.