How do I use Voice Changer on mac?

I heard you use antares voice, Virtual audio cable to input voice on game on steam, and acoustica to mix voice on a PC,These are all pc things. I figured out i already have garage band which is just like acoustica, and a vitual audio thing like this (link decribes more)

http://support.apple.com/kb/HT1215?viewlocale=en_US&locale=en_US

How do I use voice like antares.autotune On a game multiplayer steam game like CSS or Garrysmod or TF2. This is what im trying to do. Also How do i Move it to garage band and input on the mac settings like in link.

Pleae Help,

-Gary