Forward req’s from i’net to private IP?

I have a small network with a Windows 98se machine doing internet sharing for a cable modem. I have an application I’d like to run on a separate pc. Since all internet traffic to the private IP’s goes through the main pc with a public ip address, only the public computer can be seen from the internet. I want requests for a certain port(telnet,23) to be forwarded to a private IP computer. Can this be done with win9x os’s? I think linux can with the ipchains feature, but I’d rather stick with win9x…