If you created a reset disk before forgetting your password, insert the USB and click "Reset password" at the login screen.
A fast, text-based utility that is completely free and open-source. It works by editing the Windows SAM file to clear the password. windows vista password reset usb free download
If you are completely locked out, you will need a second working computer to download these tools and "burn" them to a USB drive. If you created a reset disk before forgetting
If you still have access to an administrator account or created a reset disk before being locked out, these are the easiest options. these are the easiest options.