Ah, okay. Well, that seems out of my league.
Best of luck.
I assume if you have FCP7, you have the other portions of the FCS, including Soundtrack Pro (STP).
What I do is bring the video into FC and add it to the timeline. I then will double click the audio portion and zoom in to a spot I can easily mark, like a cymbal crash, etc., then I mark that spot. Then I add the secondary audio to the timeline and do the same thing, both at the start and end of the song. I can now see if the marks line up on the timeline. If they do not, I see how many frames are needed to make the secondary audio match. Then I open that audio in Soundtrack Pro. I select all the audio in STP, and from the Process menu, I choose Time Stretch. From there I can make the adjustments. Saving the file and quitting out of STP will result in the files being altered in the FCP timeline nondestructively, of course. Then you can just delete the primary audio from the timeline and output to your format of choice.
I hope the above helps.
There is also Singular Software's products which do a really great job. You can d/l a trial. I like the standalone version better than the one that works from within FCP.
keytohwy