CookieContainer ck = NetUtils.GetUriCookieContainer(new Uri("http://www.tuourl.it"));
            CookieCollection cl = ck.GetCookies(new Uri("http://www.tuorul.it"));
            String cookieValue = String.Empty;
            foreach (Cookie cookie in cl)
                cookieValue += cookie.Name + "=" + cookie.Value + ";";

            cookieValue.TrimEnd(';');
            System.Net.ServicePointManager.Expect100Continue = false;
            .......
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create("pagina da richiedere");
            ...
            request.Headers.Add("Cookie", cookieValue);