I think I just figured out how to allow specific ip addresses in hosting a game if you have a firewall and want certain people to still be able to play. Go to
Control Panel>Security Center>Windows Firewall> Exceptions>Click on the game you want to edit the networking options for>Click Edit>Change Scope>Then click Custopm list and type in the addresses for which you'd allow. But then again the top option might be better, which is automatically chosen anyways....hmmm so why doesn't it work in the first place?

My old D-Link router did this quite easily. I went into the firewall and created a port forward based on the port number used by the game. The forward would not only refer incoming traffic on that port to the PC in my LAN hosting the game, but I could also set it to accept incoming traffic from

a) Any/all IP address
b) A range of IP addresses
c) One specific IP only

Personally, I've never used the built in Windows Firewall. Like a lot of their software, it's bulky and balky and has a tendency to either not do what you want, or if it is capable of doing so, the setup for it is much more involved than it needs to be.

Take some advice. Buy a decent SOHO router (mine was D-Link DI 604) and shut the Windows firewall off.

What if I don't know the port number the game uses? Is there a way to open up all port for a specific IP address? And would this allow us to play each other in Jedi Knight, or would we both have to do port forwarding on our modems?