Below are a few examples you might want to try... did a little cutting/pasting and didn't try to compile, but should work fine.   Wrote these methods a few years ago and have been working fine since.  

public class HttpPost
 {
        static public string GetResponseAsString( string url, int timeout )
        {
            HttpWebRequest webRequest = (HttpWebRequest)System.Net.WebRequest.Create( url );


            webRequest.AllowAutoRedirect = true;
            webRequest.Timeout = 1000 * 30;
            webRequest.UserAgent = "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)";
            webRequest.PreAuthenticate = true;
            webRequest.Credentials = CredentialCache.DefaultCredentials;

            webRequest.Proxy = new System.Net.WebProxy("your proxy server", true); // comment out if you're not going thru a proxy

            WebResponse webResponse = null;

            try
            {
                webResponse = webRequest.GetResponse();

                Stream stream = webResponse.GetResponseStream();

                Encoding encoding = System.Text.Encoding.GetEncoding( "utf-8" );

                StreamReader streamReader = new StreamReader( stream, encoding );

                string result = streamReader.ReadToEnd();
                return result;
            }
            catch ( Exception e )
            {
                return  e.Message;
            }
        }

        static public HttpWebResponse GetResponse(string url)
        {

            HttpWebRequest webRequest = (HttpWebRequest)System.Net.WebRequest.Create(url);

            webRequest.Proxy = new System.Net.WebProxy("your proxy server", true); // comment out if you're not going thru a proxy
            webRequest.AllowAutoRedirect = true;
            webRequest.Timeout = 1000 * 30;
            webRequest.UserAgent = "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)";
            webRequest.PreAuthenticate = true;
            webRequest.Credentials = CredentialCache.DefaultCredentials;
            return (HttpWebResponse)webRequest.GetResponse();
        }
}