function openCenterWindow(theURL,winName,features,width,height) { 
  popup_left = (screen.width / 2) - (width/2);
  popup_top = (screen.height / 2) - (height/2);

  features = features + ",width="+width+",height="+height;
  features = features + ",top="+popup_top+",left="+popup_left;
  features = features + ",titlebar=0";
  window.open(theURL,winName,features);
};

function showWindow(e,url){ 
   var x=y=0; 
   if (e != "") 
     { 
     x = e.screenX; 
     y = e.screenY; 
     } 
   finestra = window.open(url,'nome_finestra','width=160,height=150,screenX=' + x + ',screenY=' + y + ',left=' + x + ',top=' + y); 
};