var http_request;
var bAJAX = true;
crearAJAX ();

function crearAJAX ()  {
	http_request = false;
	
	if (window.XMLHttpRequest) { // Mozilla, Safari,...
		http_request = new XMLHttpRequest();
		if (http_request.overrideMimeType)
			http_request.overrideMimeType('text/xml');
	}
	else if (window.ActiveXObject) 
	{ // IE
		try {
		     http_request = new ActiveXObject("Msxml2.XMLHTTP");
		} catch (e) 
		{
			try {
				http_request = new ActiveXObject("Microsoft.XMLHTTP");
			} catch (e) {}
		}
	}

	// No se pudo crear instancia XMLHTTP. Se utilizará versión sin AJAX.
	if (!http_request) {
		bAJAX = false;
		return false;
	}
}

function chkState ()
{
	var contenedor = document.getElementById ('contenedor');
	
	if (http_request.readyState == 4)  {
		contenedor.innerHTML = http_request.responseText;
	}
}