function createMarker(point, img, w, h) {
  var marker = new GMarker(point);
  GEvent.addListener(marker, "click", function() {
    marker.openInfoWindowHtml("<img src='http://www.carstenjost.de/google/img/" + img + "' width=" + w + " height=" + h + ">");
  });
  return marker;
}
function readXml(file) {
	GDownloadUrl(file, function(data, responseCode) {
	  var xml = GXml.parse(data);
	  var markers = xml.documentElement.getElementsByTagName("marker");
	  for (var i = 0; i < markers.length; i++) {
	  	var point = new GLatLng(parseFloat(markers[i].getAttribute("lat")),
					parseFloat(markers[i].getAttribute("lng")));
	  	var file = markers[i].getAttribute("file");
	  	var w = markers[i].getAttribute("w");
	  	var h = markers[i].getAttribute("h");
		map.addOverlay(createMarker(point, file, w, h));
	  }
	});
}