You need to give us more info.
Judging by what you said, all you need is a hub or switch, 3 cat5 cable's, and a nic in each comp.
The IP addy of 1 comp will be 192.168.0.1, the next 192.168.0.2 and the third 192.168.0.3
192.168.0.*** is a private range of addresses set aside for private networks (like yours)
Otherwise, talk to some of the networking expertz
