function getBox(num){
  var ret = null;

  switch (num){
    case 1: ret = document.b_1; break;
    case 2: ret = document.b_2; break;
    case 3: ret = document.b_3; break;
    case 4: ret = document.b_4; break;
  }

  return ret;
}


function replaceImage(box_num, image_fname){
  var box = getBox(box_num);

  if (box != null){
    box.src = box.src.replace(/[a-zA-Z0-9_\-\.]+\.jpg/, image_fname);
  }
}

function PopUp(url) {
window.open(url,"MyPopup",'height=600,width=600,toolbar=no,location=yes,directories=no,status=no,menubar=no,scrollbars=no,resizable=0'); 
}


function changeImage(box_num, link_num){
  replaceImage(box_num, "link" + link_num.toString() + ".jpg");
}


function restoreImage(box_num){
  replaceImage(box_num, "box" + box_num.toString() + ".jpg");
}