Melissa345b,
Each copy of XP can only be used on one computer at a time. If the copy of XP that you bought at WalMart is currently being used on another computer besides the new laptop, then you can't install that same Windows on the new laptop.
Look on the bottom of the laptop and tell us if there is a Certificate of Authenticity, if so, post the edition of Windows that it is for. Don't post the Product Key. Also tell us the make and model of laptop you have.