Have you run the wizard on the main PC to use Internet Connection Sharing? On the 2nd PC, in the internet options, connections, set it to "never dial a connection", and in LAN Settings, select "automatically detect settings". This should make the 2nd PC get its IP address from the main PC.
Run the wizard on both PCs, this tells them both that the 2nc PC will be getting its IP address etc off the main PC, thats how ICS works with the main PC dishing out the IP addresses. As for settings, once u do the wizard and the 2nd PC goes on the net, then if they are required. you can put them in then. HTH