It seems to me at one time that I read something on a Microsoft web site about an add-in for IIS which would allow you to host a couple of different services on the same public IP address and port combination. I can't find that information again. The software would accept requests and then direct traffic to the appropriate server. So, for example, you could have Exchange and Remote Desktop Web Access running on the same public IP address. The feature I am referring to would route the web request to the correct back end server.
Do you know what product or feature I am thinking of?