If it came preinstalled as an add-on to XP, you will have to contact HP.
But I doubt if they would even know about it now.
https://en.wikipedia.org/wiki/Microsoft_Plus!
Marketed as "The Ultimate Photo, Music, and Movie Enhancement Pack for Windows XP", Microsoft launched Plus! Digital Media Edition along with Windows XP Media Center Edition. Plus! Digital Media Edition signified the first time Microsoft had released a second Plus! product based on the same base operating system. Microsoft Plus! Digital Media Edition was also the first Microsoft product to be made available for sale to consumers via e-commerce as full product download through online retailers
To find your XP operating system product key:
Compaq is HP.
If OEM preinstalled (Dell, HP, etc.) license:
The COA sticker, which has the Product Key on it, is either on the underside of the Laptop or in the Battery Compartment.
With a Desktop it is either on the side, rear or top of the Computer Case.
