Counterstrike - how to force it to use my external IP for a server?

[Shag]

I am trying to figure out how I can setup a CS server (non-dedicated) on my machine, but am having problems. I have 2 NICs in my machine, and when I create a game, CS wants to use my internal IP address instead of my external one. Is there any way I can force it to use the external IP?

Thanks.