how to find XP sp2 cd key?

[wowzer]

I know that the manufacturer is supposed to put my CD key (or whatever number) on the laptop. Unfortunately, that label is rubbed off and now I need to reinstall XP off of the install disk that came with the laptop. However, I cant find the number on the laptop's hard drive (properties), get info. Is there a way to find this info?

I'm doing this for my friend's laptop--and he has even less ideas on windows machines than I do.

Thanks.