This is a great question, The ICS server should protect it's self, but I don't think it can protect the client.
The ICS is acting as a router, which makes me think it will, but will it apply it's own firewall settings to
traffic that it's passing...
I wouldn't play around, on the Win 2003 turn on IPSec the outbound Nic, block all traffic that you don't want the out-bound nic card to pass. Done SLAM dunk. <full stop>
I'm doing something similar at my work...
Two XP machines, on doing the data collection, one presenting it on a web page using Microsofts personal web services.
The world will see the web server and it's as restricted as I can make it.
The PC to PC lan, is much less restricted but I will still blocked all the unneaded ports.
Was a big job to eliminate all unnessary ports and still have it work, some diging was required to find all the ports needed....
I have it working with Microsoft Firewall...
But
I will still turn-on IPSec.
I will buy a buy a personal firewall and lock down the same ports.
I will lock the IE6 menu settings on both PCs two...
Why? Defence in Depth...
If a hacker gets past one barrier he has many more to go.
Oh and my web server is just presenting data gathered by the second PC, but I want it to stay up, everyday, and not to be hijacked..
Brian