I'm trying to change my voice on Skype using this tutorial http://www.erzsabet.com/mySLSound.html, which I got working with GarageBand '09. However, I just bought GarageBand '11, and there doesn't seem to be any vocals software instrument. Where can I find them, please?
There are Vocal Effects in Garageband. Open Garageband and create a voice project:
Then go to the Info pane in the bottom right hand corner:
Under Real Instrument>Vocals, you will find all the effects you were looking for.