var objCount = 0; // number of (changing) images on web-page

function preload(name, first, second) {  

  if (browserOK) {     
    pics[objCount] = new Array(3);
    pics[objCount][0] = new Image();
    pics[objCount][0].src = first;
    pics[objCount][1] = new Image();
    pics[objCount][1].src = second;
    pics[objCount][2] = name;
    objCount++;
  }
}

function on(name){
  if (browserOK) {
     for (i = 0; i < objCount; i++) {
      if (document.images[pics[i][2]] != null)
        if (name != pics[i][2]) { 
          // set back all other pictures
          if (pics[i][0].complete)
            document.images[pics[i][2]].src = pics[i][0].src;
        } else {
            // show the second image because cursor moves across this image
            if (pics[i][1].complete)
              document.images[pics[i][2]].src = pics[i][1].src;
        }
    }
  }
}

function off(){
  if (browserOK) {
     for (i = 0; i < objCount; i++) {
      // set back all pictures
      if (document.images[pics[i][2]] != null) 
        if (pics[i][0].complete)
            document.images[pics[i][2]].src = pics[i][0].src;
    }
  }
}

preload("link1", "images/1.jpg", "images/1_on.jpg");
preload("link2", "images/2.jpg", "images/2_on.jpg");
preload("link3", "images/3.jpg", "images/3_on.jpg");