Well, I am in the same boat. I have a music track and a few voice overs so I need to lower the audio in the music track when the voice over cuts in, and raise the audio when the voice over finish. I've been using Pinnacle Studio but have recently converted to Mac OS X and now using iMovie09. It's a shame that you cannot split the audio track, or that iMovie does not allow you to make changes to the wave format in the track.. The only work around I found was to note at what section (timewise in the music track) the audio needs lowering/raising and then use a wave editor (eg wavepad) to vary the audio volume. Then save the music track under a different name (so as not to change the original) and use that in the iMovie project. Works, but only when done as the last step before publishing the movie since the changes are sort of 'locked in'. Let me know if you find any easier way of doing this.