function switchImage(img,which)  {
    if (which == 0)
      {  img.src = "images/" + img.name + "_off.gif";  }
    else if (which == 1)
      {  img.src = "images/" + img.name + "_over.gif";  }
    else
      {  img.src = "images/" + img.name + "_on.gif";  }
  }