if (document.images) 
{
      img1 = new Image();
      img2 = new Image();
      img3 = new Image();
      img4 = new Image();
      img1.src ="images/attendance_over.jpg";
      img2.src ="images/finance_over.jpg";
      img3.src ="images/study-tours_over.jpg";
      img4.src ="images/button_more_over.gif";
}