/* image preload */
if (document.images)
{
  pre_pic1= new Image(106,106);
  pre_pic1.src="images/uulogo24_on.png";
  
  pre_pic2= new Image(195,17);
  pre_pic2.src="images/nav00_ani.gif";
  
  pre_pic3= new Image(230,17);
  pre_pic3.src="images/navbox_ani_bgl.gif";
  
  pre_pic4= new Image(230,17);
  pre_pic4.src="images/navbox_ani_bgr.gif";
}

/* swap function  */
<!--
function imgSwap(oImg)
{
   var strOver  = "_on"    // image to be used with mouse over
   var strOff = "_off"     // normal image
   var strImg = oImg.src
   if (strImg.indexOf(strOver) != -1) 
      oImg.src = strImg.replace(strOver,strOff)
   else
      oImg.src = strImg.replace(strOff,strOver)
}
//-->