What I am trying to is have a navigational drop down menu on my main.swf and when a user presses the button in the drop down menu it will load an external swf file into a blank movie clip. This is pretty easy. The hard part is targeting the drop down buttons in the main.swf file to target specific frames of the external swf file. I can do this with variables and have been successful but I want an if statement where if looks to see if the swf is already loaded into the empty movie clip, if it is then just gotoAndPlay and specific frame, but if it's not I want it to go to my preload movie clip and then load the external movie.
is there a way to tell what external swf file is loaded into the movie clip? Something like

if _root.emptymovieclip=externalfile.swf;
_root.emptymovieclip.gotoAndPlay("about")
}else{
_root.preload.gotoAndPlay