var ua = navigator.userAgent.toLowerCase(); 

   // browser name
   this.isOpera       = (ua.indexOf('opera') != -1); 
   this.isIE          = (ua.indexOf('msie') != -1 && !this.isOpera && (ua.indexOf('webtv') == -1) ); 
   this.isFirefox     = (ua.indexOf('firefox') != -1);
   this.isNS          = (ua.indexOf('netscape') != -1);
   this.isMac    = (ua.indexOf('mac') != -1);


 if (this.isFirefox == true) {
  document.write('<link rel="stylesheet" href="templates/style_firefox.css" type="text/css">');
}
 if (this.isNS == true) {
  document.write('<link rel="stylesheet" href="templates/style_firefox.css" type="text/css">');
}
if (this.isOpera == true) { 
  document.write('<link rel="stylesheet" href="templates/style_opera.css" type="text/css">');
}
if (this.isMac == true) { 
  if (this.isIE == true) {
    document.write('<link rel="stylesheet" href="templates/style_macIE.css" type="text/css">');
  }
  else {
    document.write('<link rel="stylesheet" href="templates/style_mac.css" type="text/css">');
  }

}