function roll_over(img_name, img_src)
   {
   document[img_name].src = img_src;
   }

function preload() {
  if (!document.images) return;
  var ar = new Array();
  var arguments = preload.arguments;
  for (var i = 0; i < arguments.length; i++) {
    ar[i] = new Image();
    ar[i].src = arguments[i];
  }
}