if (document.images) {
  im01a = new Image();
  im01a.src = "img/im1_a.gif";
  im01n = new Image();
  im01n.src = "img/im1_n.gif";
  im02a = new Image();
  im02a.src = "img/im2_a.gif";
  im02n = new Image();
  im02n.src = "img/im2_n.gif";
  im03a = new Image();
  im03a.src = "img/im3_a.gif";
  im03n = new Image();
  im03n.src = "img/im3_n.gif";
  im04a = new Image();
  im04a.src = "img/im4_a.gif";
  im04n = new Image();
  im04n.src = "img/im4_n.gif"
}