Recording the sound of my Mac
Solution 1:
Rogue Amoeba's Audio Hijack Pro can do this for you and much more.
Solution 2:
If you want to do it for free you can download Audacity and Soundflower (if you have a mac) and record the sound straight off your sound card.
Audacity: http://audacity.sourceforge.net/download/
Soundflowerbed: http://cycling74.com/downloads/
Tutorial: http://wiki.audacityteam.org/wiki/User:BillWharrie/Using_Soundflower_to_record_streaming_audio
You mentioned you're using a mac, but for people who run windows, there is likely another program you can substitute for Soundflower to accomplish the same thing, although I have not looked into it.
Solution 3:
Another option, also from Rogue Amoeba, is Piezo which is about 50% the cost of Audio Hijack Pro. So, depending on how complex your needs are, there are two really great options.