function changebackimageNN(id,img){
  if(document.layers){
      document.layers[id].background.src=img;
  }
  if(document.all){
      document.all[id].style.backgroundImage="url("+img+")";
  }
  if(!document.all&&document.getElementById){
      document.getElementById(id).style.backgroundImage="url("+img+")";
  }
}