var xmlHttp

function mostrar_calendario(){ 
var r = document.getElementById('vmes').value ; 
var r2 = document.getElementById('vmes2').value ; 

xmlHttp=GetXmlHttpObject();
if (xmlHttp==null)
  {
  alert ("Su navegador no soporta AJAX!");
  return;
  } 
var url="mostrar_calendario.asp";
url=url+"?r="+r + "&r2=" + r2;
xmlHttp.onreadystatechange=stateChanged;
xmlHttp.open("GET",url,true);
xmlHttp.send(null);
}

function stateChanged() 
{ 
if (xmlHttp.readyState==4)
{ 
document.getElementById("textotabla").innerHTML=xmlHttp.responseText;
}
}

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;
}