How to Configure the ICS Host Computer - Windows 2003

The ICS host computer provides a connection through the second network adapter to the existing TCP/IP network. Log on as member of the Administrators group to set up the ICS host computer.

1. Click Start, click Control Panel, and then click Network Connections.
2. Right-click Local Area Connection (the network card that you just installed), and then rename it The Internet Connection.In the Network and Dial-up Connections dialog box, two connections are displayed (for different network adapters): The Internet Connection and Local Area Connection.
3. Right-click The Internet Connection, and then click Properties.
4. Click the General tab, and then verify that Client for Microsoft Networks and Internet Protocol (TCP/IP) are displayed.
5. Click the Advanced tab, and then click to select the Enable Internet Connection Sharing for this Connection check box.NOTE: Make sure that firewall software or other Internet sharing software from any third-party manufacturer have been removed.
6. Click OK, and then return to the desktop.

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Thanks to  http://techgurulive.com/2009/03/09/how-to-configure-the-ics-host-computer-windows-2003/