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) {
  nav01_over = newImage("images/nav01_home_on.gif");
  nav02_over = newImage("images/nav02_about_on.gif"); 
  nav03_over = newImage("images/nav03_cctv_on.giff");
  nav04_over = newImage("images/nav04_additional_on.gif");
  nav05_over = newImage("images/nav05_products_on.gif"); 
  nav06_over = newImage("images/nav06_contact_on.gif");
  
  preloadFlag = true;
 }
}