Help! How to Record Audio Playing on MacBook

Hi I am in broadcasting and conduct several interviews through Google Voice and Skype. I just got my new MacBook and I am having major problems trying to figure out how to record audio playing through my speakers with my microphone. I tried both Audacity & Garage Band. I'm lost using Soundflower and I feel like I've read so many blogs on this topic that I've been twisted and turned way too much. I'm hoping someone can provide some step by step solutions.

Here's what I've done (I have 2 issues I need corrected)

For recording interviews:

When Soundflower is open I selected "Built in Output" under the 2 channel, then I created an Aggregate Device in the Audio MIDI set up and am using the Soundflower and my USB mic as inputs for the device. When I try to record in Audacity or Garage Band I am able to pic up my mic but not the sound playing through the computer.

I also stream live shows and events and need to be able to play commercials from iTunes during breaks. The set up is basically the same.

I created another Aggregate Device with my external equipment and Soundflower both listed as inputs.

If anyone can solve these issues for me I would really appreciate it!

You should look at either Audio Hijack Pro ($32) or WireTap Studio ($69) -- think of them as beautiful front ends to Soundflower, far easier to use.

As for playing commercials I'd suggest a "cart machine" like Soundboard ($50). There are a number of other options out there at various price points, take a look around and see what's recommended by others.