My Lord you sure are worthy of your title! I downloaded a copy of Mac Army Knife and followed your instructions to the letter. It worked perfectly - every download now plays after they have been through the software. Many thanks to you and others for all your help.
One last small question. My daughter has a PC, do I have to change the Creator and File Type entries ('MPG3' and 'Hook') for her to play them on her PC? Thanks again!