Windows 2000

I have a small home network consisting of an old netserver running win2k a dell gx1 running win2k and a home built box running win98se. The problem I am having is that after I set up ICS on the netserver my modem will dial-up all on its own. I made painstakingly sure that nothing was running on any of the three machines that would require internet access. It will dial-up periodically for no apparent reason. Am I missing something?