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.