No, anything that says "Clean Install" or "Erase" will delete EVERYTHING.
I believe once you pop in Snow Leopard onto your Mac, those options to Erase everything are hidden (so people don't accidentally select them).
Once you pop in your disc, it will just Upgrade your Mac if you just follow the on-screen guide. After that, you will have all your apps, pictures, music, movies etc. still on your Mac - but now you have Snow Leopard.