function abrir_ventana (destino, nombre, ancho, alto) {
	var url = destino;
	var w = ancho;
	var h = alto; 
	var menu = "no";
	var scroll = "yes";
	var tool = "no";
	var location = "no";
	var resize = "no";

	var winl = (screen.width - w) / 2;
	var wint = (screen.height - h) / 2;
	winprops = 'width='+w+', height='+h+', top='+wint+', left='+winl+', menubar='+menu+', scrollbars='+scroll+', toolbar='+tool+', location='+location+', resizable='+resize+''
	window.open(url, nombre, winprops);
	
	return;
}