If by software, you mean configuration. If you just want to get the machines up and running (and talking) and are not worried about sharing an internet connection (good place to start, just to make sure things are working correctly) Give the three machines the following IP addresses (You can do this during setup):
machine #1 - 192.168.10.10
machine #2 - 192.168.10.11
machine #3 - 192.168.10.12
Those are private addresses, which are reserved for private networks not connected to the Inet.
If you want to connect all three machines to the Internet and you have a broadband connection, I suggeset the Linksys cable/dsl router/firewall. For newbies, it's a lot easier then trying to configure your Linux box as a router, or any of the other available options. I'll explain more about that option l8r if you're interested........
