if (document.images) {
  var nav_1 = new Image();
  nav_1.src = "nav/nav_1.jpg";
  
  var nav_1a = new Image();
  nav_1a.src = "nav/nav_1_over.jpg";

  var nav_2 = new Image();
  nav_2.src = "nav/nav_2.jpg";
  
  var nav_2a = new Image();
  nav_2a.src = "nav/nav_2_over.jpg";

  var nav_3 = new Image();
  nav_3.src = "nav/nav_3.jpg";
  
  var nav_3a = new Image();
  nav_3a.src = "nav/nav_3_over.jpg";
  
  var nav_4 = new Image();
  nav_4.src = "nav/nav_4.jpg";
  
  var nav_4a = new Image();
  nav_4a.src = "nav/nav_4_over.jpg";
  
  var nav_5 = new Image();
  nav_5.src = "nav/nav_5.jpg";
  
  var nav_5a = new Image();
  nav_5a.src = "nav/nav_5_over.jpg";
  
  var nav_6 = new Image();
  nav_6.src = "nav/nav_6.jpg";
  
  var nav_6a = new Image();
  nav_6a.src = "nav/nav_6_over.jpg";
  
}

function act(imgName) {
  if (document.images) 
    document.images[imgName].src = eval(imgName + "a.src");
}

function inact(imgName) {
  if (document.images)
    document.images[imgName].src = eval(imgName + ".src");
}