function GetXmlHttpObject()
{
  var xmlHttp=null;
  try
    {
    // Firefox, Opera 8.0+, Safari
    xmlHttp=new XMLHttpRequest();
    }
  catch (e)
    {
    // Internet Explorer
    try
      {
      xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
      }
    catch (e)
      {
      xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
      }
    }
  return xmlHttp;
}

function enviar(xmlHttp,url,valores){
	var tipo="GET";
	if(valores!=null)
		tipo="POST"
	xmlHttp.onreadystatechange=stateChanged;
	xmlHttp.open(tipo,url,true);
	if(tipo=="POST")
		xmlHttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
	xmlHttp.send(valores);
}