works on windows XP
I never tried on windows 7 or vista but feel free to try.
1. restart your computer
2. when you see those things like Admin or users etc just press f8
3. category will be shown
4. choose safe mode
5. then choose windows xp or what OS you are currently using
6. some words will pop out but just ignore it
7. click on the account you want to get in to(no need for password on this stage)
8. go to control panel>Users
9. then remove or change the password you can also remove the password there.
10.reboot again and its done.
*If your on Safe mode you don't need the Admins password, you can go with out using prompting to a password then you can go directly to the control panel then users then remove the password and reboot, after that you don't need to do safe mode again because the password is already removed.
just try if it works =)