Hola andy, tienes varias formas:
<html>
<head>
<script language="JavaScript">
<!--
function detecta ()
{
document.write("Navigator: "+navigator);
document.write("<br>Nombre: "+navigator.appName);
document.write("<br>Version: "+navigator.appVersion);
document.write("<br>Codename: "+navigator.appCodeName);
}
//-->
</script>
</head>
<body onLoad="detecta();" bottommargin="0" marginheight="0" marginwidth="0" rightmargin="0" topmargin="0" leftmargin="0">
</body>
</html>