compatibilité ajax/ie

<script language="JavaScript" type="text/javascript">

function getXhr() {
var req = null;

//firefox
if (window.XMLHttpRequest) {
req = new XMLHttpRequest();
}

//ie
else if (window.ActiveXObject) {
try {
req = new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e) {
req = new ActiveXObject("Microsoft.XMLHTTP");
}
}

//non supporté
else {
alert("Fonction non supportée par le navigateur");
req = false;
}

return (req);
}

function getTrack()
{
var req = getXhr();

req.onreadystatechange = function() {

if (req.readyState == 4 && req.status == 200) {
var resultat = req.responseText;
document.getElementById('div_track').innerHTML=resultat;
}

};

req.open("GET","http://generationsfm.com/ajax_track.php?act=track",true);
req.send(null);
setTimeout("getTrack()", 5000);
}

getTrack();
</script>

<?
switch ($_GET['act'])
{
case "track":

$html = simplexml_load_file('http://generationsfm.com/sms/Titres.xml');
foreach($html->WhatsOn as $WhatsOn) {
$titre = $WhatsOn->Titre;
$artiste = $WhatsOn->Chanteur;
}

echo $titre." - ".$artiste;
break;
}
?>