document.write('<link rel="stylesheet" href="'); 
var agt=navigator.userAgent.toLowerCase(); 
if (agt.indexOf('opera') != -1) document.write('opera.css'); 
else if (agt.indexOf('gecko') != -1) document.write('mozilla.css'); 
else if (agt.indexOf('msie') != -1) document.write('msie.css'); 
else document.write('msie.css'); 
document.write('" type="text/css">');