Routing with Mutiple NICs in XP

Setup: 2 Cable modems, 1 Linksys router, 1st NIC hooked directly to one cable modem, 2nd NIC through a linksys router then to the 2nd cable modem.
Problem: Want to route all traffic that uses a specific port through one NIC, and the 2nd NIC is used for everything else. Is there a way to do this in XP, or is there specific software (firewall?) that can manage this.