function popupCentrato(mypage, myname, w, h, scroll)
{
    var winl = (screen.width - w) / 2;
    var wint = (screen.height - h) / 2;
    winprops = 'height='+h+',width='+w+',top='+wint+',left='+winl+',scrollbars='
        +scroll+',resize=no';
    win = window.open(mypage, myname, winprops);
    if (parseInt(navigator.appVersion) >= 4) 
    { 
        win.window.focus(); 
    }
}