Soundfly is a very little utility that just sends the audio of one Mac to another, using built-in Mac OS X Tiger technologies, and Soundflower.
It comes as a package containing an application that sends to audio over the network (Soundfly), and another that receives and plays the audio stream (Soundfly receiver). It works out of the box, but if you want further configuration, press ALT when launching either application: you'll be able to configure the Audio Units.
Soundfly is freeware. You can freely distribute it without modification. However, if you want to support the author (me), you can make a donation by clicking on the link below. Thank you!