function newImage(arg) {
   if (document.images) {
      rslt = new Image();
      rslt.src = arg;
      return rslt;
   }
}

function changeImages() {
   if (document.images && (preloadFlag == true)) {
      for (var i=0; i<changeImages.arguments.length; i+=2) {
         document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
      }
   }
}

var preloadFlag = false;

function preloadImages() {
   if (document.images) {
      nav_over1 = newImage("/fileadmin/bwinf/noflash/bwinf-biber.jpg");
      nav_over2 = newImage("/fileadmin/bwinf/noflash/bwinf-bundes.jpg");
      nav_over3 = newImage("/fileadmin/bwinf/noflash/bwinf-einstieg.jpg");
      nav_over3 = newImage("/fileadmin/bwinf/noflash/bwinf-ioi.jpg");
      preloadFlag = true;
   }
}