The problem with playing MP3 files with QT Player is that, if they have been played with any other MP3 player, their file types and creator codes make them unrecognizable to QT Player. Personally, I always used Vamp, so my codes are MP3! and MP3!. I have about 300 MP3 files stored on a CD, all typed to match Vamp. So, if I want to play them with QT player, I have to copy them to the hard drive first, then change their file types, then play them, then dump them when I'm through. Every time I want to play any of them, I have to do this all over again. A pain.
I propose that Apple add translators to the final version of QT4 so that we can open any MP3 file from any player in QT Player. That way, I don't have to remaster another CD and dump the one I have.