loadMovie on alternating levels?

Basically I have several external swfs I am loading into one swf. For the navigation purposes, I need to load these swfs onto levels. There will be two at a time and I can’t find script to load these swfs on two specified levels. I need to check if level 1 is occupied, and if it is, load on level 2. If level 2 is occupied, I need to load on level 1. How could I go about doing this?

Thanks!