function bookmark() {
  var agt=navigator.userAgent.toLowerCase();

  
  var is_win = (agt.indexOf('windows')!=-1);
  var is_mac = (agt.indexOf('mac')!=-1);

  var is_ie     = (agt.indexOf('msie') != -1);
  var is_firefox = (agt.indexOf('firefox') != -1);
  var is_netscape  = ((agt.indexOf('mozilla')!=-1) && (agt.indexOf('compatible') == -1));
  var is_safari = ((agt.indexOf('safari')!=-1)&&(is_mac));

  if (is_win) 
    if (is_ie && window.external) 
      window.external.AddFavorite(location.href,document.title);
    else 
      if (is_firefox) 
        alert('Please press CTRL + D to bookmark this page.');
      else 
        if (is_netscape) 
          alert('Please press CTRL + D to bookmark this page.');
        
        else 
          alert('Please press CTRL + D to bookmark this page.');
  else 
    if (is_mac) 
      if (is_ie && window.external) 
        window.external.AddFavorite(location.href,document.title);
      else 
        if (is_safari) 
          alert('Please press Command (Apple) + D to bookmark this page.');
        else 
          alert('Please press UP arrow + Command (Apple) + D to bookmark this page.');
    else 
      alert('Please press CTRL + D to bookmark this page.');
  return false;
}