Mishy, don't use ICS. Its a total pain, and messes up your comps. The easiest way to share internet between your two computers is to use WinProxy. It is easily configured. Actually when you install it, it tells you which addresses to assign your NIC cards and the subnet.
Just make sure all your computers can see each other on the network. Peer to Peer IP is the easiest. Then install WinProxy on the computer with the internet connection, and carefully read the text info it generates.
MOST importantly before doing any of this is to uninstall ICS before anything.