How to access internet on another network

i have a 1.1 networka and a internet router on a 3.1 network. In the past I was able to put the rounter ip as the gateway and the isp DNS on a 1.1 PC and have internet on the 1.1 PC. It was a linksys rounter. That one broke and I have what i think is the same kind and now i cant do it. Am I Crazy? What setting should I look for?