Audacity doesn’t do anything in real time except capture/record. That is a very old feature request.
If you’re doing all this in post production, then there’s hope. Several people make voice changing software you can apply after you record your voice.
BrotherSoft
http://www.brothersoft.com/av-voice-changer-software-diamond-24729.html
MorphVOX
http://www.rocketdownload.com/program/morphvox-classic-voice-changer-25642.html
AV Voice Changer
http://www.softbuy.com/av-voice-changer-software-gold-3005.html
Voice Imitation
http://www.filesland.com/companies/Voice-Imitation-Recognition-Ltd/Vocal-Imitation.html
Koz