I remember that this was mention a lot when the iMac and Airport was new. But there hasn’t been much talk about using a Mac as an Airport Base Station to network computers.
This site has instructions on how to set this up. Of course, if you are going to need a network for long time service you are better off with an Airport Extreme.
This site gives 8 steps to do on each computer that is to be connected to the network. Of course, the one of those 8 is, decide which computer is to be the host, connected to a wired port. So once you get the first one setup, there are really only 7 steps.
See it all here.
