var agent = navigator.userAgent.toLowerCase(); 
var ver = parseInt(navigator.appVersion); 

if ((agent.indexOf("mozilla") != -1) && (ver <= 4) && (navigator.appName.indexOf("Netscape") != -1)) 
{document.write('<LINK HREF="styles/ns.css" REL="stylesheet" TYPE="text/css">');
}

if ((agent.indexOf("mozilla") != -1) && (ver > 4) && (navigator.appName.indexOf("Netscape") != -1)) 
{document.write('<LINK HREF="styles/ie.css" REL="stylesheet" TYPE="text/css">');
}

if ((agent.indexOf("mozilla") != -1) && (ver >= 4) && (navigator.appName.indexOf("Microsoft") != -1) ) {
document.write('<LINK HREF="styles/ie.css" REL="stylesheet" TYPE="text/css">');
}