Post to form doesn't work

[logik3x]

Hi, I'm making a program to send grades to a website we use at our
school. My problem is I can't get to post data to the site...

string uri = "http://brebeuf.omnivox.ca/";
HttpWebRequest myHttpWebRequest =
(HttpWebRequest)WebRequest.Create(uri);
myHttpWebRequest.CookieContainer = new CookieContainer();
HttpWebResponse myHttpWebResponse =
(HttpWebResponse)myHttpWebRequest.GetResponse();
myHttpWebResponse.Close();

string postData =
"formEtudiant=o&NoDA=000000&NIP=PASS&x=0&y=0";
byte[] byte1 = Encoding.UTF8.GetBytes(postData);
HttpWebRequest myHttpWebRequest2 =
(HttpWebRequest)WebRequest.Create(myHttpWebRespons e.ResponseUri);
myHttpWebRequest2.ContentType =
"application/x-www-form-urlencoded";
myHttpWebRequest2.ContentLength = postData.Length;
myHttpWebRequest2.Method = "POST";
myHttpWebRequest2.CookieContainer =
myHttpWebRequest.CookieContainer;
myHttpWebRequest2.AllowAutoRedirect = true;
Stream newStream = myHttpWebRequest2.GetRequestStream();
newStream.Write(byte1, 0, byte1.Length);
newStream.Close();

If I analyse the http packet wih a sniffer I can see that the
Content-Length is 44 like the it should be but the form data is 0
bytes.