Don't try lie.
Xp can't do this only if its a Illegal copy and the guy at the shop would not risk his business for people like you, he actually would own a Legit copy of xp that he can put on so many computers.
Don't try come here and get answers of how to crack threw it, yes their is a way but please go else where, Here at CF we do not discuss things such as Illegal computer works and business's