thought you'd like that ;)

yups - red wire = right channel, blue = left channel, black = ground

The program uses a 'bit-banging' technique, toggling the output pins high and low to create the squarewave output.

you can check out the sketch here -
blog.makezine.com/archive/2008/08/arduinoise_beats.html

but the real credit goes to Loud Objects, who wrote the original code from which this is derived -
loudobjects.com/kit/