Hi there, sorry for the late reply
Normally you can set up your connection type while creating a profile when running the game for the first time. Just click on the connection type word (e.g.: local, modem ... etc) to toggle between connection types.

On a side note, which mac version are you running? There have been issues with Macbooks version 10.5 not being able to run the game.
If that's the case, download the following config file I created a while ago when having that issue:

A lot of Mac users have a problem with their ET not running correctly (not to say not at all). When they run ET they'll hear a buzzing sound and ET shuts off. This Autoexec file can help you solve that problem. Download it and save it into your ET main, run ET and normally it will work. (This is used for Apple MacBook)
Download (click)

Be sure to notify us if you fixed your problems