I am not the worlds expert on QT but that is not the program I would have chosen to convert LP's to Digital. Something like Audion or CD Spin Doctor (comes free with Toast) would be much better suited to audio editing than QT.
Although you can probably do it, it's going to be busy. I guess you bigger file is the entire LP of, for instance, 8 tracks. You are trying to separate the tracks. Into separate Files or what?
Separate files would involve setting the pointers to select the track, Copy Selection, Make a new File, Paste. That does nothing for the quality of the audio though and is hard work. An Audio editing suite, Audion is free, is capable of taking your entire file and cleaning it up. Removing rumble and hiss and making the spaces between the track, clean. If you have already imported the file, I guess you have, Audion will still open it and you can export to a number of different formats.

Let us know if this is what you are trying to do.

P