[BigDan]

function check(mc:MovieClip){
  var upY:Number=Stage.height/2+(mc._height/2-Stage.height/2);
  var downY:Number=Stage.height/2-(mc._height/2-Stage.height/2);
  var rightX:Number=Stage.width/2+(mc._width/2-Stage.width/2);
  var leftX:Number=Stage.width/2-(mc._width/2-Stage.width/2);
  if(mc._y>=upY){
    mc._y-=4;
  }
  if(mc._y<=downY){
    mc._y+=4;
  }
  if(mc._x>=rightX){
    mc._x-=4;
  }
  if(mc._x<=leftX){
    mc._x+=4;
  }
}