function random_banner(){
  var i=0;
  banners = new Array();
  banners[0] = '<IMG SRC="images/header1.jpg" WIDTH=891 HEIGHT=252>';
  banners[1] = '<IMG SRC="images/header2.jpg" WIDTH=891 HEIGHT=252>';
  banners[2] = '<IMG SRC="images/header3.jpg" WIDTH=891 HEIGHT=252>';
  today = new Date();
  i=today.getSeconds();
  n=banners.length;
  return banners[i-Math.round((i-1)/n)*n];
}