function  initialize() {
  if (GBrowserIsCompatible()) {
   map = new GMap2(document.getElementById("map_canvas")); 
   map.setCenter(new GLatLng(20.659364,-103.396185),15);
   map.addOverlay(new GMarker(map.getCenter()));   
   map.addControl(new GSmallZoomControl());
  }
}

Event.observe(window, 'load', function () { initialize();});