IPTables: How can I make all traffic to a certain subnet go through one interface while all other traffice goes through another?

Say I have two network interfaces and both are connected. The OS still routes everything through one connection as far as I can tell, unless the application (or something beneath it like ip tables) alters that. I have one computer, with a static ip if that helps, that I need to route all traffic through another interface than the main one. Ideally I could route it by the subnet as it wouldn't require if the ip were static, and in case I were to add other computers it would be more versatile. I'm sure this can be done, but I really don't know iptables at all, google was no help, and the manual is daunting. Thanks guys.