If you use xp and upgrade to vista, your XP cd key is no longer valid, and i think when you update to vista again it will not work since when you upgraded to vista your voided your xp cdkey. So you can really only upgrade once i think.... I will look for a source later if needed. No I didn't use the XP product key. I used the product key that come with the laptop. It was under the bottom of the laptop.