function activar(url, id_contenedor){
var pagina_requerida = false
if (window.XMLHttpRequest) {
pagina_requerida = new XMLHttpRequest()
} else if (window.ActiveXObject){ 
try {
pagina_requerida = new ActiveXObject("Msxml2.XMLHTTP")
} 
catch (e){ 
try{
pagina_requerida = new ActiveXObject("Microsoft.XMLHTTP")
}
catch (e){}
}
}
else
return false
pagina_requerida.onreadystatechange=function(){ 
cargarpagina(pagina_requerida, id_contenedor)
}
pagina_requerida.open('GET', url, true) 
pagina_requerida.send(null)
}

function cargarpagina(pagina_requerida, id_contenedor){
document.getElementById(id_contenedor).innerHTML="<table width='100%' height='100%' border='0' cellpadding='0' cellspacing='0'><tr><td bordercolor='#0000FF'><div align='center' style='background-color:#FFFFFF'>Cargando<br><br><img src='images/cargador.gif' width='45' height='45' /></div></td></tr></table>";	
if (pagina_requerida.readyState == 4 && (pagina_requerida.status==200 || window.location.href.indexOf("http")==-1))
document.getElementById(id_contenedor).innerHTML=pagina_requerida.responseText
}