Internet Connection Sharing (ICS) with 2 PCs and 1 host?

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When you turn on Internet Connection Sharing {ICS} on the host computer, the host computer's LAN adapter is automatically assigned the IP address of 192.168.0.1. Therefore, one of the following situations may occur: IP address conflict because each computer on the LAN must have a unique IP address. If more than one computer has the same IP address, an IP conflict occurs, and one of the network adapters turns off until the conflict is resolved. To resolve this conflict, configure the client computer to automatically obtain an IP address, or assign it a unique IP address.

If this doesn't resolve the problem try the Microsoft Help Database with keywords ICS/Internet Connection Sharing {multiple computers}.