Its totally illegal to do that. Soliciting people in the intent of giving away window's key is illegal no matter how you attempt to say its not or maybe. IT IS! Check out the Terms of Service/License.
The licenses are probably activated anyway....it has to be within 30days. Schools do that (attach the key on the side) because if things need to be updated or changed the key is right there and not in 30 different places.
My advice: DONT DO IT!
You want to take away profit from Microsoft then create a o/s thats better lol[/i]
Actually, they're probably not activated. The school probably has volume licensing for XP Pro and the PCs came by default with XP Home. It's possible the XP Home keys are manufacturer specific, similar to the way you can't use a Dell Windows XP CD to install Windows XP on a non-Dell PC.
Regardless, the school owns the licenses so it's a federal crime to give one of the product keys to someone. I don't see how this constitutes frivilous spending anyway, since it's almost impossible to buy a PC without a Windows license these days.
The long and short of it is if the OP's friend really needs Windows XP, then he can buy it like everyone else.