Reinstalling Aperture 2 under Snow Leopard
To reinstall Aperture 2 under Snow Leopard from scratch you'll need a copy of the full Aperture 2.1.4, or at least of the trial version, but it has to be the full package, not just the update. And you won't find it on Apple's Website, now that Aperture 3 is available. But you can find it here.