[BigDan]

Что-то вроде этого:

var attached:Boolean=false;
btn.onRollOver=function(){
  if(!attached){ 
    attachMovie("linkage","help_mc",_parent.getNextHighestDepth());
    attached=true;
  }
  help_mc._x=_xmouse;
  help_mc._y=_ymouse;
}
btn.onRollOut=function(){
  help_mc.removeMovieClip();
  attached=false;
}