if you'be got the ADSL modem connected to the "server pc" then you will need to share the internet connection, has your router not got an DSL port? if not and you are planning to share the net connection, then you will need to enable ICS (internet connection sharing) on "the server" pc, to do this right click the connection you want to share in network connections select properties and then advanced place a tick in enable ICS, the second thing you need to do is to set the ip address's, "the server" or the machine sharing the connection must have it's IP address set to 192.168.0.1, but from what you've told me, with the adsl modem connected to "the server" the router is unecessary, as you could just create a p2p (peer to peer) network, ideally you want the adsl modem connected to the router to create and infrastructure.
J