You are sharing your internet connection with the Server 2003 machine? Or do the clients connect to the Cisco directly?
Either way, if you want some decent statistics, then you have to set up a proxy on your server and force people to use that. You may have to attach some extra software to get pretty summaries from the proxy logs.
If you are satisfied with huge listings of from-socket,to-socket pairs, then you can probably get the infor from the Cisco router. With ICS, this is imposible without some extra sotware.