Just a guess, but you might find that he is recording through the built-in microphone, something that the mini does not have.
So I'm kind of confused.
My friend has grageband on his powerbook and opened it up and then hit "record" to get sounds his computer was making. (specifically the cool sound that AIM makes when it starts).
I tried the same thing on my Mac Mini and it wouldn't record any ambient sounds at all. When I would create a new track and try to record on it it would say something along the lines of "this track isn't set to record.
Going back to my friend to show me exactly what he did, I tried to emulate his actions perfectly. Either I was wrong, I have some setting on or off that he has otherwise or there is something screwed up wih my computer.
(I have the latest version of Garage Band and belive he does also)
Any clue why I'm not able to record ambient computer made sounds?