Wired? Do any of you have a router that you can all connect to? You'll need some cat5 cable too. If all you have is a hub or a switch you should still be able to manage but you'll need to manually give each machine an IP address, starting with 192.168.0.1 for example.
Do you all have wireless? I've never done ad-hoc wireless networking but you can probably all link up via that without needing to buy anything.