Odd enough, I just went though something similar..
With QT4, you have the ability to edit mpg1 files, and you can also do it in QT5 (OS9/OSX), but with QT6 Apple totally removed the option to edit them. (anyone know why?)
I installed QT 6 Pro then just pulled my QT5 player from my backup and use that for cutting my MPG files.
In QT5, just move the 2 sliders to the part you want to keep, then drag the image of the movie to your desktop. once you have the clippings you want to keep, open the first one, then drag and drop you other clippings into the viewier window, they will get added to the timeline.
you then need to export the whole thing as a MPEG1 file again.
it can be very time consuming, I personally would rather just fast forward through the commercials.