problema con req.responseXML.getElementsByTagName

[websalacarta]

ante todo muchas gracias

here it is:

Código:

var req;

function initRequest(url) {
    if (window.XMLHttpRequest) {
        req = new XMLHttpRequest();
    } else if (window.ActiveXObject) {
        isIE = true;
        req = new ActiveXObject("Microsoft.XMLHTTP");
    }
}



function calculateResult() {
    var url = "lib/ajax.php?material=" + document.getElementById("materialid")+
    					"&size="+ document.getElementById("sizeid")+
    					"&side1Colour="+ document.getElementById("side1Colourid")+
    					"&side2Colour="+ document.getElementById("side2Colourid")+
    					"&SPS="+ document.getElementById("SPSid")+
    					"&finishing="+ document.getElementById("finishingid")+
    					"&frontCover="+ document.getElementById("frontCoverid")+
    					"&backCover="+ document.getElementById("backCoverid")+
    					"&sets="+ document.getElementById("setsid");
    initRequest(url);
    req.onreadystatechange = processRequest;
    req.open("GET", url, true); 
    req.send(null);
}


function processRequest() {
    if (req.readyState == 4) {
        if (req.status == 200) {

					//document.getElementById("resultid").innerHTML  = req.responseXML.getElementsByTagName("price")[0].childNodes[0].nodeValue;
					alert('aa');
					alert(req.responseXML.getElementsByTagName('price')[0].item(0).nodeValue);
  				//alert(req.responseXML.getElementsByTagName('price')[0].firstChild);
       }
    }
}