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_company_over = newImage("images/nav_company-over.gif");
  nav_clients_over = newImage("images/nav_clients-over.gif");
  nav_work_over = newImage("images/nav_work-over.gif");
  nav_disciplines_over = newImage("images/nav_disciplines-over.gif");
  nav_philosophy_over = newImage("images/nav_philosophy-over.gif");
  nav_contact_over = newImage("images/nav_contact-over.gif");
  preloadFlag = true;
 }
}