If you’ve got the Second Life Voice Beta, you’ll have been freaked out like I have. It’s all a bit weird. People used to stand around saying talking shit before, but now that they have voices, it’s doubly weird. Triply weird. Check it out.
Anyway, voice disguise will be important if you want to even try to maintain some distance between you and your avatar. And you can do it for free with the software that came with your Mac, and the free software Soundflower. It’s a bit tricky with the current beta, though, as SL gives you no choices of sound inputs — it just uses the system defaults.
The process, if you want to test it, is to set Garageband to take your microphone as input, and to use SoundFlower (2ch) as output. In Garageband, make a new vocal track and turn monitoring on. Set up your voice the way you want with the vocal transformer. Male to Female, Female to Male, Monsters, Echo, Reverb, whatever.
You then go to System Preferences and set Soundflower (2ch) as the default input, and your headphones as output. Launch SL. It should get everything from the System defaults and should work well. You will hear yourself all the time, but you’re only public when you’re holding the push-to-talk key and the speaker symbol above your head is flashing. Enjoy!