function objetoAjax (){
	var xmlhttp=false;
	try {
		xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
	} catch (e) {
		try {
			 xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
		} catch (E) {
			xmlhttp = false;
			}
	}

	if (!xmlhttp && typeof XMLHttpRequest!='undefined') {
		xmlhttp = new XMLHttpRequest();
	}
	return xmlhttp;
}
function peticion_ajax (url, params, contenedor) {
	/*//donde se mostrará los registros
	divContenido = document.getElementById(contenedor);
	ajax = this.objetoAjax();
	//url = 'index.php';
	ajax.open("POST", url+'?rdm='+Math.floor(Math.random()*10000), true);
	//ajax.setRequestHeader('Content-Encoding', 'UTF-8'); 
	ajax.onreadystatechange=function() {
		if (ajax.readyState==4 ) {
			divContenido.innerHTML  = ajax.responseText;
			alert(url);
			alert(ajax.responseText);
		}
	}
	ajax.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
	ajax.send(params);	*/
	divContenido = document.getElementById(contenedor);
	ajaxPetition(url, params, function (ajax) {
		divContenido.innerHTML = ajax.responseText;																		
		//alert(ajax.responseText);
	});
}
function ajaxPetition(url,params,callback){
	if(!url){return;}
	if(!params){params="";}

	var rnd = Math.floor(Math.random()*10000);
	var ajax = new objetoAjax();
	ajax.open("POST",url+"?rnd="+rnd,true);
	ajax.onreadystatechange=function(){
		if(ajax.readyState==4){
			callback(ajax);
			return;
		}
	}
	ajax.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
	ajax.send(params);
}