Yes, you can install the Lion Server "app" on any Mac as far as I know. It's just an add-on to the OS now, for an extra $40 or so from the mac app store. I was reading some article where the author was running it on his Macbook Pro.

You will also want to find and download the server admin tool for Lion, which is a separate, free download from Apple. It has the firewall configuration for the server. On mac-os X client, that's in 'settings'. But not on the server. The server runs a different type of firewall. The normal server app will modify the firewall configuration for you, but there are some things you might want to enable. I think under snow leopard server I had to modify it to allow itunes sharing to work from the server, for example. There's good documentation on all of that stuff on support.apple.com.

-David