function openwindow(url, wnd_name, width, height)
{
    if (top[wnd_name]!=null && typeof(top[wnd_name])=='object' && !top[wnd_name].closed && top[wnd_name].load_flag==1)
    {
        if (top[wnd_name].document.location.href!=url) top[wnd_name].document.location.href=url;
        top[wnd_name].focus();
    }
    else
    {
        top[wnd_name] = window.open(url, wnd_name, 'width=' + width + ',height=' + height + ',status=no,menubar=no,resizable=yes,scrollbars=yes,left=' + String((screen.width-width)/2) + ',top=' + String((screen.height-height)/2));
    }
}