stylo = navigator.appName;

if (navigator.userAgent.indexOf("Mac") != -1) { 
                sCSS = '<LINK REL=StyleSheet HREF="/style/mac.css" TITLE="Main" TYPE="text/css">';
}
else if (stylo == "Netscape") { 
                sCSS = '<LINK REL=StyleSheet HREF="/style/net.css" TITLE="Main" TYPE="text/css">';
}
else {
                sCSS = '<LINK REL=StyleSheet HREF="/style/ie.css" TITLE="Main" TYPE="text/css">';
}
document.write(sCSS)