Having trouble with Garage Band Built-in Input

I'm fiddling around with GB, I understand the difference between the built-in mic and the built-in input, but the simple computer mic i have in the audio input jack is showing no signs of responding whatsoever. I have the monitor turned on in GB and nothing. I also tried checking the general audio input in the System Preferences. It's entirely possible this computer mic is busted, but I've used it before on my old PC and it was fine. Any ideas would be really appreciated because that built-in mic blows on many levels.




Oh and also, just so we're clear, the audio input jack is the one directly adjacent to the headphones/output jack, right? I'll sing if that's all I'm doing wrong.

 

All right, thanks! And now that I think of it, that sounds like more of what I've seen other people with, and they had either a mixer to go through, a sound card, or a nice condenser mic with its own power source. Supposing I find a USB mic, though, will GB recognize that as another "Built-in Input"?