Network setup question

(I'm a University student who unfortunately has very limited funds to purchase a router. I wanted to preface this question with that note because my problems would be fixed if I could get one)

Anyway, I have 1 network connection in my dormitory. We are only allowed one connection and under some flimsy guidelines, we aren't allowed to use routers. Fortunately, I have extra NIC cards to use.

Here is the scenario - I have a PC and a Mac. PC has two NICs and in my grand scheme, I'd like it to be the mac plugged into the PC which is plugged into the wall.
Wall <=PC<= MAC

I have everything set up correctly (physically with XOvers) and successfully have used the Mac to surf the web. However, when I install a software firewall (comodo) that is using rules wizard or active learning, it shuts down the connection to my mac.

I set this entire network up using ICS in the XP's network connection properties on my PC=>Wall NIC. It apparently bridged the connections for the MAC=>PC connection and is sitting happily next to a "bridge connection" icon. (As you can tell from my diction, I am quite a newb).

Any who, my issue is how to set up this comodo program in order to allow my mac full access to the web while still protecting my PC from the pseudo hackers and port scanners in my dormitory.

I only have the IP of my machines and COmodo did do an auto setup for trusted zones, but I'm not entirely sure what to do with these. I've messed around with them several times using possible IP ranges, but have had little luck.

Any help would be appreciated.

Cheers,
E