I want to load an external swf into an mc that is above another mc........HELP

It seems fairly basic.
I want to load in an external swf into an mc that is above another mc. Once the new swf is loaded in, I want the lower one to be set to _visible = false.

How would I set this up? Is it a matter of swapping depths?

Each time a button is clicked, I want the new file to be loaded in on top.

I was thinking of doing something with levels, so that I load it into the current level + 1. Is that even possible or a good approach. There are infinite levels right?
Thanks,