function preloader() {
  homeImage = new Image(); 
  homeImage.src = "images/top_home.gif";
  homeImageOn = new Image(); 
  homeImageOn.src = "images/top_home_on.gif";

  newsImage = new Image(); 
  newsImage.src = "images/top_news.gif";
  newsImageOn = new Image(); 
  newsImageOn.src = "images/top_news_on.gif";

  applyImage = new Image(); 
  applyImage.src = "images/top_apply.gif";
  applyImageOn = new Image(); 
  applyImageOn.src = "images/top_apply_on.gif";

  contactImage = new Image(); 
  contactImage.src = "images/top_contact.gif";
  contactImageOn = new Image(); 
  contactImageOn.src = "images/top_contact_on.gif";

  tabImage = new Image();
  tabImage.src = "images/tab.gif";
  tabImageOn = new Image();
  tabImageOn.src = "images/tab_on.gif";
}

function randomImage() {
  var randImage = new Array();
  randImage[0] = "headerGraphicHome1";
  randImage[1] = "headerGraphicHome2";
  randImage[2] = "headerGraphicHome3";
  var randNumber=Math.floor(Math.random()*3); 
  document.getElementById("headerGraphic").id = randImage[randNumber];
}