Separating Audio from other Audio

I have a video of a friend giving a speech that has apparently been previously overlayed with a music track. I am trying to seperate these two different audio forms in order to get just the speech, in order to lay it onto my own music track. Do any of you have any ideas on how I may accomplish ithis on my MacBook Pro? The video is currently in (.mov) format. I am not a novice at working with this media, but by no means a pro.
I am not a beginner at working with this media, but am, by no means, an expert. I am pretty new to the Mac world, , I have tried a tiny bit (without success) on iMovie and GarageBand.
Any help would be greatly apprecitated.
Thank You Very Much!

If the music is already overlaid on the video, there's really nothing much you can do apart from trying to minimize it a bit. Use the equalizer to bump up the midrange tones and lower the highs and lows. That's about it, other than smacking the person who did that to the video about the head.