Hi John,
If you have a Windows Vista installation disk, you can reinstall Windows Vista. If you do not have a disk, you may need to contact the computer manufacturer to know how to regain Windows Vista.
Information: Most OEM computers have a recovery feature and you can use that feature to restore the computer to its factory settings. In this way, you may be able to regain Windows Vista. If you would like to know how to use that feature, please contact your computer manufacturer.
Hope it helps.
Best regards,
Tim Quan
Microsoft Online Community Support