I am using Google maps example from book, and from Google
documentation.  It is really simple, and I don't know why isn't
working.  My browser send mi this response:

This XML file does not appear to have any style information associated
with it. The document tree is shown below.
<markers id="id je ok">
<marker found="Keychain" lat="37.441" left="Book" lng="-122.141"/>
<marker found="Water Bottle" lat="37.322" left="Necklace"
lng="-121.213"/>
</markers>

My code is following
var getVars =  "?q=" + search;
var request = GXmlHttp.create();
request.open('GET', '/lbs/' + getVars, true);
request.onreadystatechange = function() {
  if (request.readyState == 4) {
    var xmlDoc = request.responseXML;
    alert(xmlDoc);
    var responseNode = xmlDoc.getElementsByTagName('markers').item(0);
    var type = responseNode.getAttribute("id");
  }