If you're instantiating the sound with code you can just use embed metadata to do the trick. It works like this (all code assumed to be in a class):
[Embed(source = 'loop.mp3')]
private var MusicClass:Class;
private var music:Sound = new MusicClass();
Then just instantiate music and off you go!
This doesn't affect the FLA at all or make compile time that much longer.
Note that you'll have to have the Flex SDK (which is free) installed somewhere on your machine to use this. Flash will prompt you for it's location the first time you compile.
Branden Hall
2009-09-16 17:46:19