Network Connection Running Fine Ics Cannot Work

Ive just had broadband connected to my house. Currently I have a network consisting of four computers connected through an internal switch on one of my computers in one of the bedrooms for ease of cabling. The computer with the broadband modem has been chosen as it is newest and is closest to the telephone line socket. It has two network cards, one connected to the modem and the other to the rest of the network. Independantly, the network connections are running fine (all computers can see each other and transfer data properly) and the internet connection is working well for the computer connected directly to the modem.

The network is setup using Static IP Addresses 192.168.0.1-192.168.0.4 (With 0.1 being for the host) and the modem is connected using a different set of IP addresses. I have also set the internet connection sharing options according to what is required on the microsoft website for both the internet host and clients. I have both Norton Antivirus and Zonealarm activated on all computers but have set them up to allow access to each other. My problem therefore is, despite my broadband connection working on the one computer, and my network connections working, I cannot get ICS to work.