Espero este te funcione
Código PHP:
<script language="JavaScript">
<!--
function MM_checkBrowser(NSvers,NSpass,NSnoPass,IEvers,IEpass,IEnoPass,OBpass,URL,altURL) { //v4.0
var newURL='', verStr=navigator.appVersion, app=navigator.appName, version = parseFloat(verStr);
if (app.indexOf('Netscape') != -1) {
if (version >= NSvers) {if (NSpass>0) newURL=(NSpass==1)?URL:altURL;}
else {if (NSnoPass>0) newURL=(NSnoPass==1)?URL:altURL;}
} else if (app.indexOf('Microsoft') != -1) {
if (version >= IEvers || verStr.indexOf(IEvers) != -1)
{if (IEpass>0) newURL=(IEpass==1)?URL:altURL;}
else {if (IEnoPass>0) newURL=(IEnoPass==1)?URL:altURL;}
} else if (OBpass>0) newURL=(OBpass==1)?URL:altURL;
if (newURL) { window.location=unescape(newURL); document.MM_returnValue=false; }
}
//-->
</script>
</head>
<body bgcolor="#FFFFFF" text="#000000" onLoad="MM_checkBrowser(4.0,2,2,6.0,1,2,0,'entrada.html','noentras.html');return document.MM_returnValue">