Connectivity between two ethernet interfaces

Im configuring a G4/400 Mac OS X Server with two ethernet interfaces/adaptors (both 100/10 first ´en0ª built-in, second ´en1ª assantÈ on PCI slot 3) both interfaces have its own tcp address and configuration, both have assignated its own network port. I have runned geekrouter, but I CANT access to the second port address devices. I mean, if I choose ´en1ª on the top of ´Network Port Configurationª (Network Preference Pane) I can see this net, and if I, indeed, choose ´en0ª on the top of ´Network Port Configurationª I can see that net. BUT I CANT never see both nets. I cant connect to any device/address of the second port of the list. I though with a router I could make a solution, I tried to config through ipfw on terminal too, but, is sure, Im doing something bad.