Network Issue

When I setup the NTP service, I downloaded a time set program to each of the four client machines in the house (3 on Win 2K, 1 on Win ME). Two of the machines were able to connect to my time server, while the other two couldn't find it. I instead set them up to use a server at work.

Now, when I try to use the X-Server, the same two machines that could connect to NTP can connect via XDMCP just fine. The third Win 2K machine can see the server, but the Linux login screen never appears.

I wonder if there is some networking issue on these two machines that is causing the problem. All four are using ZoneAlarm and are setup the same way. I can ping the Linux server from all as well. I'll do a little experimentation today and see what I can find.