var btn_a = new Array(10);
  var btn_b = new Array(10);
  var buttonDesc = new Array(10);

  buttonDesc[0] = "Home";
  buttonDesc[1] = "Casino history";
  buttonDesc[2] = "How to play";
  buttonDesc[3] = "Top 50 casinos";
  buttonDesc[4] = "Play games";
  buttonDesc[5] = "Free offers";
  buttonDesc[6] = "Las Vegas casinos";
  buttonDesc[7] = "Testimonials";
  buttonDesc[8] = "Email";
  buttonDesc[9] = "Add to favorites";

for(var x=0; x<8; x++){
  btn_a[x] = new Image(); 
    btn_a[x].src = "images/btn" + (x+1) + "a.gif";
  btn_b[x] = new Image();
    btn_b[x].src = "images/btn" + (x+1) + "b.gif";
}

  btn_a[8] = new Image();
    btn_a[8].src = "images/email_a.gif";
  btn_b[8] = new Image();
    btn_b[8].src = "images/email_b.gif";

  btn_a[9] = new Image();
    btn_a[9].src = "images/favorites_a.gif";
  btn_b[9] = new Image();
    btn_b[9].src = "images/favorites_b.gif";

function imageOn(num){
  document.images["btn" + num].src = btn_b[num].src;
return  window.status = buttonDesc[num];
}

function imageOff(num){
  document.images["btn" + num].src = btn_a[num].src;
}