I have 3 computer set up in a network. they are not connected to the internet. I'm using them with a track program. I ping them and two of them are talking to each other but they are not talking to the third. However the third one is pinging the other two. I'm lost and don't know what to do. Need your help.

are you using automatic DCHP or have you set the TCP/IP addresses by hand. On some machines I have on a network by setting the TCP/IP addresses (different) in the usual range
192.168.1.X and onwards solved this problem for me! avoid x = 1 as many adsl routers use that!
M

In addition to mjdodd's question, Is there a software firewall on that third computer?? I have seen a software firewall block communications between computers.