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If you have the Apple authorized store reinstall your system you'll still need to get a set of the disks in case there are issues later on that would require you to use them, i.e. boot into them to repair the disk for example. Otherwise you're dead in the water until you take it back to another store for fixing. That can get pretty expensive.

Yes, they can do the reinstall. Make sure they reinstall Snow Leopard and not some other OS. And it has to be a reinstall, not a clean install. Ask them if what they will do will save everything, apps, settings, users. And pay attention to what OT wrote. You really need to get the install DVD, at least.