Usually when you set up ports in your firewall from the outside, you have to direct the traffic to a single private IP address. I haven't used the "personal" proxy servers that are an application you load on your computer, so I'm not sure if they work the same. I use a Firewall Server for my corporate network.

If you want to use the same port for multiple computers, you're either going to need a Proxy Server or Internet Sharing enabled on one of the computers. Then the other computers can connect to the Internet through that one computer.

The only problem is that the one computer has to be on for the other computers to access the Internet and the servers you're downloading from. If you use a proxy server, the computer with the proxy server software will have to be running for the other computers to access the Internet too. Either way, you'll always have to have one computer running.

You can configure multiple ports to use with your client, one set for each computer. This is probably your best best since you'll only have to have one computer on at any one time.

Good luck!