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) {
    home_over = newImage("/images/ui/nav/home-over.gif");
    home_down = newImage("/images/ui/nav/home-down.gif");
    timeline_over = newImage("/images/ui/nav/timeline-over.gif");
    timeline_down = newImage("/images/ui/nav/timeline-down.gif");
    authors_over = newImage("/images/ui/nav/authors-over.gif");
    authors_down = newImage("/images/ui/nav/authors-down.gif");
    perspectives_over = newImage("/images/ui/nav/perspectives-over.gif");
    perspectives_down = newImage("/images/ui/nav/perspectives-down.gif");
    resources_over = newImage("/images/ui/nav/resources-over.gif");
    resources_down = newImage("/images/ui/nav/resources-down.gif");
    loa_over = newImage("/images/ui/nav/loa-over.gif");
    loa_down = newImage("/images/ui/nav/loa-down.gif");
    preloadFlag = true;
  }
}