Is it possible to download Snow Leopard?
Unless you're part of the Apple Developer Program, or you have access to a server running in an enterprise environment that is licensed to distribute copies of OS X, no.

Since OS X Lion is newly released, you will likely find less and less support for Snow Leopard from this point forward.  Lion is, as of now, distributed ONLY via download, so you may want to consider just getting Lion unless you need Snow Leopard for a spec