What you want to do is stream the mp3's from an external source.
use soundobject.loadSound("urlto.mp3",true) to "stream", which plays as it loads, not packet streaming like winamp.
You can use the onSoundComplete event to execute code when flash finishes playing a sound.
or if you are using continuous play, load on exit, etc you can use something like:
Trying to load that many files with the movie is going to take forever... although I haven't seen a format where you couldn't use a preloader.
my_sound = new Sound(this);
You can always use a preloader, even if it loads an external swf, the preloader doesn't have to be inside the loading swf