Some time ago the laptop was dropped - it was fine for a while, but then over time the sound recording quality worsened to the point that it just sounded like harsh static. Neither the internal mic nor the audio jack nor a USB mic worked any more for recording sound. The one time I took it in to the Apple store, it suddenly started working again when the tech took it in the back room; tapping on the internal mic sometimes seemed to help.

I did a full reformat and reinstall of 10.5, and it upgraded to 10.5.6, and then I tried to use Skype with internal mic and jack, to no effect. I don't think it could possibly be a driver issue with a totally clean reinstall.