I'm looking to use software under OSX to act like a Lexicon Jamman.

Basically, what I want to do is play my guitar, loop the phrase, then continue to play over my first loop and keep doing that. I would like to do the same with voice, so that I could build up a song to the point where I am playing guitar and singing with myself!

Anyone know how I might achieve this?

Look at the POLAR module included into Digital Performer, it'd be just what you need.
MOTU

Thanks.The MOTU guy at the Apple Expo said the same thing, but he couldn't get it right. He eventually said he didn't think Polar could do it plus we couldn't figure out how to activate the loop with a guitar in your hand. There didn't seem to be a way to start recording via a midi pedal on the ground. Do you have any other info?