function ajaxFunction() {
	var xmlHttp;
	try {
	// Firefox, Opera 8.0+, Safari
	xmlHttp=new XMLHttpRequest();
	return xmlHttp;
	} catch (e) {
	// Internet Explorer
		try {
		xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
		return xmlHttp;
		} catch (e) {
			try {
			xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
			return xmlHttp;
			} catch (e) {
			alert("Tu navegador no soporta AJAX!");
			return false;
			}
		}
	}
}

function enviar(_pagina,capa) {
	var ajax;
	ajax = ajaxFunction();

	ajax.open("POST", _pagina, true);

	ajax.setRequestHeader("Content-Type",
	"application/x-www-form-urlencoded");
	ajax.onreadystatechange = function() {
		if (ajax.readyState == 4) {
			if (ajax.status==200) {
				document.getElementById(capa).innerHTML =
				ajax.responseText;
			}
		}
	}
	ajax.send(null);
}