HOW TO ADD MULTIPLE AUDIO TRACKS - iMovie '11

I'm having trouble adding multiple audio tracks in iMovie 11. I already have an audio track embedded with the video and a separate music track under. I wish to extend the music track further but need to cut it off at a certain point. I tried just adding the 2nd music track under the first but when I 'drop' the track it doesn't show up anywhere. Any ideas or work arounds will be helpful. Thanks.