Can't get XML data to javascript?

[garethhall]

Hello Guys I have page I am working on but my xml object is null? well it's null when I do an alert? Can you guys see something work?

 

Javascript

var xmlHttp
function getMemDetail(){
xmlHttp=GetXmlHttpObject()
if(xmlHttp==null){
	alert("Browser does not support HTTP Request");
	return;
}
var qstr;
qstr = "memID="+document.getElementById('members').value;
xmlHttp.onreadystatechange = returnDetails;
xmlHttp.open("POST","ajax/getMemberDetails.php?",true);
xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xmlHttp.send(qstr);
}
function returnDetails(){ 
if(xmlHttp.readyState==4 ){ 
	//alert(xmlHttp.responseText);
	//xmlDoc = xmlHttp.responseXML;
	alert(xmlHttp.responseXML);    //WHY IS THIS NULL
		document.getElementById("toName").innerHTML = xmlDoc.getElementsByTagName("memFirstName")[0].childNodes[0].nodeValue;
}
} 

function GetXmlHttpObject(){
var xmlHttp=null;
try{
	// Firefox, Opera 8.0+, Safari
	xmlHttp=new XMLHttpRequest();
}catch (e){
	// Internet Explorer
	try{
		xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
	}catch (e){
		xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
	}
}
return xmlHttp;}

 

PHP

<?php
include("../../includes/cmsConfig.php");
include("../../includes/sharedFunctions.php");
auth();

$sql = "SELECT * FROM members WHERE memID = ".checkVars($_POST['memID']);
$rs = mysql_query($sql ,$admin);
$rw = mysql_fetch_assoc($rs);


echo '<?xml version="1.0" encoding="ISO-8859-1"?>';
echo '<member>';
echo '<memName>'.$rw['memName'].'</memName>';
echo '<memFirstName>'.$rw['memFirstName'].'</memFirstName>';
echo '<memLastName>'.$rw['memLastName'].'</memLastName>';
//	echo '<memAddress>'..'</memAddress>';
echo '</member>';
?>