function getXMLHttp(){
  var xmlHttp;
  try {
    //Firefox, Opera 8.0+, Safari
    xmlHttp = new XMLHttpRequest();
  }
  catch(e)  {
    //Internet Explorer
    try{      
		xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
    }
    catch(e){
      try{
        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
      }
      catch(e){
        alert("Your browser does not support AJAX!")
        return false;
      }
    }
  }
  return xmlHttp;
}
function MakeRequestCity(url, from_where){
  var xmlHttp = getXMLHttp();
  var waitImg = document.getElementById("imgloader");

  xmlHttp.onreadystatechange = function()
  {
	if (xmlHttp.aborted==true) { 
	  return;
	}
  	
    if(xmlHttp.readyState == 4 && xmlHttp.status == 200)
    {
	  waitImg.style.display =  'none';	// to stop to show the imagen "ajaxLoader.gif"
      HandleResponse(xmlHttp.responseText, from_where);
    }
    else
    {
		waitImg.style.display =  'block'; 	// to show the imagen "ajaxLoader.gif"
    }
  }
  xmlHttp.open("POST",url, true);
  xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xmlHttp.send();

  return xmlHttp;
}