Convert xml to string with jQuery

I'm loading an xml file with jQuery ajax loader, and need to convert it to a string so that I can save it out again using PHP post variables. What is the best way to do this?

<script type='text/javascript'>

jQuery.ajax({
    type: "GET",
    url: "data.xml",
    dataType: "xml",
    success: parseXML
    });


function parseXML(xml) {

    var xml_string = jQuery(xml).text();  // (This doesn't work- returns tagless, unformatted text) 
    alert(xml_string);

}

</script>