Is this a named PC, Packard Bell, HP/Compaq, etc,. or is it a PC the shop built?
If the former, chances are it has a recovery partition on the hard drive that you use to restore the OS in case of an emergency. This partition can be activated using a CD/DVD (which should be supplied with the PC) or it can be activated, prior to Windows loading, by pressing a key (F10 on some systems) as the PC is starting.
If the latter, then they have to give you some way of restoring the system in case of a catastrophic crash. That could be a Vista disk or a DVD with an image of your system, it's up to them. You should also have the Vista serial key in either case, it's usually stuck to the side or bottom of the tower.