function preload() {
 if (document.images) {
  for (i=0; i<arguments.length; i++) {
   eval(arguments[i]+'up = new Image()');
   eval(arguments[i]+'up.src = "img/'+arguments[i]+'.png"'); //IMAGE EXTENSION
   eval(arguments[i]+'down = new Image()');
   eval(arguments[i]+'down.src = "img/'+arguments[i]+'_on.png"');}}} //IMAGE EXTENSION
   preload('home','about','resorts','contact','costs','faq','holiday','brochure'); //INSERT IMAGE NAMES

function on(Button)
 {document.images[Button].src=eval(Button + "down.src");}

function off(Button)
 {document.images[Button].src=eval(Button + "up.src");}