Dont even bother with ICS, I took a look at your diagram, and I would suggest that you goto
www.amazon.com and look for a dlink 604 broadband router. It is easy as hell to set up, works great, lasts long time and drains to the bilge. The greatest part of the 604 is that it can be controlled with a web browser, is on all the time (so when you have to do the dreaded reboot, others wont lose connection.) The really, really good thing about it is the cost. it is 39.99 with a 10.00 rebate. Best bang for your buck. Been running mine for almost 5 months now with no troubles at all.
If you have trouble setting it up or have an issue you can icq me at 112234683