Return to the shop and ask them for copies of the software. They are required to provide physical media for the software you have purchased. It's under the same ruling that allows you to make backup copies of any software you have a license for. If you purchased it online, email the company and ask them to send you either reinstall media (which will return it to a factory state) or a Windows XP disc for the machine you purchased.
TL;DR. Go back to the shop and ask for the XP disc.