var objCount = 0;
    var pics;
    pics = new Array();
    function preload(name, first, second) {  

    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){
     for (i = 0; i < objCount; i++) {
      if (document.images[pics[i][2]] != null)
        if (name != pics[i][2]) { 
          document.images[pics[i][2]].src = pics[i][0].src;
          
          } else {
           document.images[pics[i][2]].src = pics[i][1].src;
	 }
    }
}
   

function off(){
      for (i = 0; i < objCount; i++) {
      if (document.images[pics[i][2]] != null) 
      document.images[pics[i][2]].src = pics[i][0].src;
}
  }

preload("mbook", "tops/mbook1.jpg", "tops/mbook2.jpg");
preload("search", "tops/search1.jpg", "tops/search2.jpg");
preload("memoria", "tops/mem1.jpg", "tops/mem2.jpg");