function preloadImages() {
     if (document.images) {
	  var arrImg = document.images;
	  var arrTempImg = new Array();

	  for (var i = 0; i < arrImg.length; i++) {
	    if ((arrImg[i].src).indexOf("_off.jpg") != -1) {
	       arrTempImg[i] = new Image();
	       arrTempImg[i].src = (arrImg[i].src).replace("_off.jpg","_on.jpg");
    	    }
  	}
     }
}

function changeImage(moImg, state) {
   if (document.images) {
        if ((state == 'on') && (document.images[moImg].src).indexOf("_off.jpg") != -1) {
 	       document.images[moImg].src = (document.images[moImg].src).replace("_off.jpg","_on.jpg");
        }
        else if ((state == 'off') && (document.images[moImg].src).indexOf("_on.jpg") != -1) {
 	       document.images[moImg].src = (document.images[moImg].src).replace("_on.jpg","_off.jpg");
        }
   }
}