How can I get Fraps to record Skype audio?

Me and a few friends are trying to record Minecraft videos - and this is the problem. The server's working, I can record the screen using Fraps, my computer's fine with lag, and what have you - but I can't get it to record the commentary that goes on between me and my friends. How can I get Fraps to do this? I don't mind downloading any other program - as long as it isn't paid.