Line-in Jack and Microphone Headset

Okay, I got my 15" 1.5 GHz PB today, and I love it.... except the backlit keyboard doesn't work (see separate thread), and I am wondering about the line in jack. I bought iListen, without the headset because I already have a headset, that I have used with a PC using Office 2003 Speech Recognition. But I don't get any signal showing when I attempt even the Apple Speakable items with the line-in microphone. I understand that the line-in jack is set up for powered input. Does that mean that I need to run my mike through an amp and then to the PB?

Thanks.

Uh....yeah....I already tried that, before posting. I'm pretty confident that the mic has to be powered. The line-in will register a signal if I take (for example) output from a CD player. But if I swap the plug with the mic, it registers nothing. Maybe I'll just go with a USB mic and be done with it.