Авторизация на сайте средствами HttpWebRequest

Imports System
Imports System.IO
Imports System.Net
Imports System.Text
Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
  
        Dim req As Net.HttpWebRequest = Net.HttpWebRequest.Create("http://mail.rambler.ru/mail/index.cgi")
        Dim header As New System.Text.StringBuilder()
       
        Dim cookie As String = req.GetResponse().Headers("set-cookie")
       
        req.Credentials = CredentialCache.DefaultCredentials
       
     
        req.Method = "POST"
        req.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; MyIE2;"
        req.Accept = "image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*"
        req.Headers.Add("Accept-Language", "ru")
        req.ContentType = "application/x-www-form-urlencoded"
        req.KeepAlive = False
        req.Referer = "http://www.rambler.ru/"
        req.Headers.Add(HttpRequestHeader.Cookie, cookie)
        req.AllowAutoRedirect = False
     
        Dim sQueryString As String = "from=&back=http%3A%2F%2Fmail.rambler.ru%2Fmail%2Fstartpage&url=7&login=LOGIN&domain=rambler.ru&passw=PASSWORD&long_session=on&user.password=%C2%EE%E9%F2%E8"
        Dim ByteArr As Byte() = Encoding.GetEncoding(1251).GetBytes(sQueryString)
        Dim response As HttpWebResponse = req.GetResponse()
      
        MsgBox(response.StatusDescription)
        Dim dataStream As Stream = response.GetResponseStream()
        Dim reader As New StreamReader(dataStream)
        Dim responseFromServer As String = reader.ReadToEnd()
        MsgBox(responseFromServer)
        TextBox1.Text = responseFromServer
        MsgBox(cookie)
        reader.Close()
        dataStream.Close()
        response.Close()
   End Sub
End Class