Uploading form data with WebRequest

From the chapter 14 of O'Reilly's C# in a NutShell.

WebRequest req = WebRequest.Create ("http://safari.oreilly.com/search");

req.Proxy = null;
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";

string reqString
  = "searchtextbox=webclient&searchmode=simple";
byte[] reqData = Encoding.UTF8.GetBytes (reqString);
req.ContentLength = reqData.Length;

using (Stream reqStream = req.GetRequestStream())
  reqStream.Write (reqData, 0, reqData.Length);

using (WebResponse res = req.GetResponse())
using (Stream resSteam = res.GetResponseStream())
using (StreamReader sr = new StreamReader (resSteam))
  File.WriteAllText ("SearchResults.html", sr.ReadToEnd());

System.Diagnostics.Process.Start ("SearchResults.html");