function abrir_ventana(dir,X,Y)
{ 
 var x=((screen.width)-X)/2;
 var y=((screen.height)-Y)/2;
 var tips=eval("window.open(" + 'dir' + ",'','left=" + x + ",top=" + y + ",width=" + X + ",height=" + Y + ",scrollbars=no" + "')");
}