I know you can run the server version, but neither my Lion (current) or my Snow Leopard CD I have is the server version.
Is it possible to run Snow Leopard as guest in Lion?
You're allowed to run Snow Leopard Server and Lion in a virtual machine (of course, that doesn't mean it will be easy!), but not Snow Leopard. That is, according to the EULA — it's probably possible to do this (this blog post will help you out there) — but to be compliant with the EULA, you shouldn't.