function openwindow(id, img) {
  var prefix = "?mod=obrazok";
  var pokus;
  var left = (screen.width-640)/2;
  var top = (screen.height-480)/2;
  
  prefix = prefix + "--" + id;
  if(img != null) prefix = prefix + "--" + img;
  window.open(prefix,"okno_1","menubar=no,scrollbars=no,"+"directories=no,location=no,toolbar=no,"+"resizable=yes,width=640,height=510,top=" +top+",left=" +left);
}
function showhide(id){ 
if (document.getElementById){ 
obj = document.getElementById(id); 
if (obj.style.display == "none"){ 
obj.style.display = ""; 
} else { 
obj.style.display = "none"; 
} 
} 
}