Loading XML from CPP

Hi,

 What is the best/recommended way of loading XML from a cpp mozilla application?

 {
  NS_DEFINE_CID(kXMLDocumentCID, NS_XMLDOCUMENT_CID);
  nsCOMPtr<nsIDOMXMLDocument>  pXMLDoc;
  do_CreateInstance(kXMLDocumentCID, &rv);
  pXMLDoc->SetAsync( false );
  PRBool retval = false;
  NS_NAMED_LITERAL_STRING(url , "http://mysite/myxml" );
  pXMLDoc->Load( url , &retval );
 }

 Seems to work, but then when I use the nsCOMPtr<nsIDOMXPathEvaluator> to query the XML node, I always get an empty result set(stepped down to no document owner....) So i assume this is not the way to do it anymore (used to work with Mozilla 1.4.2, but not with mozilla 1.7.2).

 What is the best/recommented practice to do this ?

 Thanks

 JM