Internet Connection Sharing (ICS)

I network my home “PC” which comprises of 5 computers. The connection is working quite ok, but the problem is that once the server is on and one of the client computers is switched on, the internet connection will be established automatically. Now, what can I do to stop the automatic connetion. I need a situation whereby connection will only be established when connection is dialled. My server is windows 2000 server while the clients is made up of winme, win2000 pro., and win98 second edition.