windows 2000 and routers

My client has workstations with win2k prof. and a win2k server with this they have micronet IP Router SP866 to access the internet. The configuration of the TCP/IP protocol of each workstation, I put the IP address of the router for the gateway and for the DNS, the IP address of the internet service provider. It works fine when they need to enter the internet but the router is always connecting to the internet spending a phone call out need, each time a computer is turned on or when accessing other stations in the network. Where am I doing it wrong? Is there a configuration that I have missed? Please do help me, it is most urgent!