flash actionscript: I am trying to create a child(sub_mc_1) mc inside a mc (main_mc_1) that is on
_level0 that will load external .jpgs. This part works fine.
main_mc_1.onLoad = function() {
this.createEmptyMovieClip("isub_mc_1", 1);
this.sub_mc_1.loadMovie("images/something.jpg");
};

The problem I am having is that I want a the emptyMC to be behind a black
frame I have built into main_mc_1. I am getting the feeling that the depth
only really works well on the _root timeline and not inside the timeline of an
existing mc. If you can help me position the empty mc behind the frame inside
main_mc_1 that would be great. I have tried afew depths and still it blocks my
frame on two sides.

You can set the depth for isub_mc1 to a very negative depth because your frame
was made in authoring so it is assigned a negative depth(don't know which one
exactly will work). You could convert your "black frame" into a movieclip, and
then use swapDepths to move it to depth 2. OR, you could make it a movieclip,
and set's linkage in the library and then use attachMovie to attach it on depth
2.