function abrirVentana(url, ancho, alto, ventana, scroll)
{
	LeftPosition = (screen.width)?(screen.width-ancho)/2:0;
	TopPosition = (screen.height)?(screen.height-alto)/2:0;
	settings = "width="+ancho+",height="+alto+",top="+TopPosition+",left="+LeftPosition+",scrollbars="+scroll+",resizable=no";
	window.open(url,ventana,settings);
}