var url = "http://www.krav-maga-center.de/includes/plz.php?plz=";

      function waehleStadt() {
         var eingegebenePLZ = document.getElementById("kf_plz").value;
         if(http_obj != "false") {
            http_obj.open("GET", url + escape(eingegebenePLZ), true);
            http_obj.onreadystatechange = verarbeiteAnfrage;
            http_obj.send(null);
         } else alert('Fehler: Konnte XMLHTTP Objekt nicht erstellen');
      }

      function erstelleAnfrage(url) {
          var http_request = false;

          if (window.XMLHttpRequest) { // Mozilla, Opera, Safari,...
              http_request = new XMLHttpRequest();
              if (http_request.overrideMimeType) {
                  http_request.overrideMimeType('text/xml');
              }
          } else if (window.ActiveXObject) { // IE
              try {
                  http_request = new ActiveXObject("Msxml2.XMLHTTP");
              } catch (e) {
                  try {
                      http_request = new ActiveXObject("Microsoft.XMLHTTP");
                  } catch (e) {}
              }
          }

          return http_request;
      }

      function verarbeiteAnfrage() {
          if (http_obj.readyState == 4) {
             if (http_obj.status == 200) {
                 var xmlDocument = http_obj.responseXML;
                 var stadt = xmlDocument.getElementsByTagName('stadt').item(0).firstChild.data;
                 var bland = xmlDocument.getElementsByTagName('bland').item(0).firstChild.data;
                 document.getElementById('kf_std').value = stadt;
                 //document.getElementById('bland').value = bland;
             } else alert('Fehler: HTTP Status: ' + http_obj.status);
          }
      }

      var http_obj = erstelleAnfrage(); // erstellen des HTTP Objektes