Now where are all the linux experts???

I want to setup a linux box to route between two networks using to nic’s. I’m at the point were I can ping both nic’s from a client. But I can not ping anything on the other side of this box from a client!! Nothing fancy running on this box. no firewall or ipmasq. Just plain simple old RedHat 7.2 with 2.4.18 kernel. Please be so kind and tell me what’s going on where am I going wrong?