function ventana(){

coordx= screen.width ? (screen.width-500)/2 : 0;

coordy= screen.height ? (screen.height-540)/2 : 0;

window.open('solicitud.php','solicitud','width=500,height=540,top='+coordy+',left='+coordx);

//window.open('solicitud.php', 'solicitud', 'width=500,height=660,top=+coordy+,left=+coordx,status=no,location=no,scrollbars=no');

}