To manually set up Internet Connection Sharing on the client computers (those not directly connected to the internet) requires a minor change to your networking setup.
To make the required change go into the networking propertis (either by right clicking on your Network icon on the desktop or via the Control Panel). From there locate the TCP/IP settings for your network adapter and go into the properties for that option. (You may need to be logged on with Administrator access to be able to do this.)
Now go to the tab labelled DNS. If there are options to enable/disable DNS make sure that you have it enabled. You then need to make sure that the IP address of the ICS server (the computer with the internet connection) is entered into the DNS Search Order list so that the ICS server will be contacted to process requests from this computer for internet access.
This article written by Stephen Chapman, Felgall Pty Ltd.