I have contacted ENSEMBLE STUDIOS regarding the issue of ICS and multiplaying with Age of Kings. Here's what they told me:
To answer your question, no, it is not possible to participate in a multi-player game with a shared or masqueraded IP address. This is because Age of Kings (AoK) uses DirectX 7.0a (specifically DirectPlay for networking). Unfortunately, DirectX 7.0a does not support IP masquerading at all. Quake III on the other hand does not use DirectX in its code-base (I believe they use winsock for networking, miles for sound, etc.). Thus you can join QIII games (though you won't be able to host them and have other people not on your network see it).
Apparently, the reason why DirectX does not support it yet is because there is no standard way that IP masquerading / Internet Connection Sharing is implemented. From what I understand, DirectX 8 is supposed to support it though.
Will you be able to play AoK on an ICS IP if you have DirectX 8 installed? The best answer I got is maybe, if you are running Win ME or Win 2k with all the service packs, but definitely not if you are running Win 98 / 95.
Are we going to support ICS users in future releases of AoK? No, the core network code of a game is not something that would even get considered as a change for something like a patch. There are simply too many things that can go wrong with changing any major system in an already released game.
AoE3? It is not a secret that we are currently working on another strategy game (RTS3 is the "official code name" ). We are definitely looking into supporting ICS connections for RTS3. I can't make any promises that it will definitely, without-a-doubt be in there, but I can tell you that it is a big concern of a lot of people around here that we are able to support it. Especially me, since I have an ICS network at home too. J
You can find more information on DirectX here: http://msdn.microsoft.com/directx/
I hope I answered all your question, write again if there is anything else I can help you with.
Quality Assurance Lead
-- So... this doesn't look so good after all for the present. Their is still some hope for games using DirectX, since they said that "MAYBE" with DirectX8 it will work. Now, when does DirectX 8 comes out? That remains to be seen. Otherwise, it will be down to the next Real Time strategy game to (again MAYBE) support ICS multiplaying online.
Seriously though, if somone out there could come up with a solution right now, right today, I'm sure that person would hit a gold mine.
Let's wait then.