Airport, Switches and NAT


So, I have a bunch of issues going on here. I use a PC and my parents use Mac. I got home for the summer a few weeks ago and have been using a setup where the parents get internet from the wireless network of the Airport Extreme, while my PC is hooked into the other ethernet port of the Airport. This was working fine, but I recently discovered that some applications I am using require me to not be behind a NAT. Apparently, hooking to the internet through the Airport puts you behind a NAT.

I am using Comcast Cable internet if that matters.

So, in order to remedy this, I attempted to hook the cable modem into the uplink port of a Linksys switch I have. Then, I plugged the Airport into the switch, and then my PC. The PC is working fine and is no longer behind the NAT, but the Macs have lost internet, even though in the Internet Connect box it says that the computer is connected to the internet through Airport.

So, there are 2 possible solutions to the problem:
1. Get the Airport to work off of a switch
2. Stop the Airport from using a NAT

I don't know how to do either of these, so any help would be great.