Clients cannot access internet with ICS

I recently set up a small network with two destop PC’s and one laptop. One of the desktops has two NIC cards installed in it in order to run ICS through my cable modem. The network portion works fine, the ICS appears to be set up fine but the clients ( one desktop and one laptop) cannot access the internet. I receive no error messages when I launch either Netscape or IE, the desktop simply never connects. The desktop with the two NIC cards(the host) connects to the internet fine. Why am I unable to connect to the internet via the client machines?