Non l'ho provato ma scritto direttamente vedi se funzia. Ciao

codice:
Tot_Load=0
Tot_Clip=3
I=1
while(I<=Tot_Clip){
    this["target"+I].contenitore.loadMovie("esterno"+I+".swf)
    this["target"+I]._alpha=0
    this["target"+I].onEnterFrame=function(){
         this.car=this.contenitore.getBytesLoaded()
         this.tot=this.contenitore.getBytesTotal()
         if(this.car == this.tot && this.car > 1024){
             // movie Caricato
            _level0.Tot_Load++
         delete this.onEnterFrame
        }
  }
I++
}

this.onEnterFrame=function(){
   barra._xscale=Math.round(Tot_Load/Tot_clip*100)
   if(Tot_clip==3){
     target1.contenitore._alpha=100
     target2.contenitore._alpha=100
     target3.contenitore._alpha=100
     delete this.onEnterFrame
  }
}