function preloadImages() {

   if (document.images) {

      imageUrl = new Array();
      imageUrl[0] = "/Images/button-inschrijven-on.gif";
      imageUrl[1] = "/Images/button-inschrijven-off.gif";

      var i = 0;
      preloadImageObject = new Image();
      for(i=0; i<=imageUrl.length; i++)
         preloadImageObject.src = imageUrl[i];
   }
}