For me, I will download the video for Youtube.com using http://keepvid.com/. I
found this website through this forum anyway, I think you can able
to perform a search on it. Then the format will be .flv after
downloaded. Then there is a converter called Total Video Converter.
It enable you to convert .flv to mp3 but it has a 15 days trial
period.
Hope it helps. 