function window_form(){
   var sw = screen.width;
   var sh = screen.height;

   var szer = sw - 640;
   var wys  = sh - 480;
   var left = szer/2;
   var top  = wys/2;
  
   window.open('formularz/index.php','formularz','toolbar=no,status=no,scrollbars=yes,location=no,menubar=no,directories=no,width=640,height=480,left=' + left + ',top=' + top);
}