Cant get shared internet to work

Hello,

I am running Win XP on 2 PC's which I am networking and and I am trying to get a shared broadband internet connection running. I have 2 NIC's on the PC connected to the broadband modem and have configured one for the internet (shared) and the second one for my home LAN which at the moment has only the second PC on it. From the PC with the two NIC's I have no problems. I can access internet with Firefox and can see the second PC's files. On the second PC I can see the gateway PC's files but I cannot get Firefox or IE to access the internet. However, I can ping Yahoo.com from the second PC through the gateway. I have spent days on this. What am I missing???

Sugarglider