求教--关于使用httpwebquest自动登陆的问题

源码如下......返回的结果是登陆的界面...而不是登陆成功后的界面....求教各位高手   
Dim cc As New CookieContainer
        Dim BAIDU_Url As String = "http://passport.baidu.com/?login"
        Dim req As HttpWebRequest = CType(WebRequest.Create(BAIDU_Url), HttpWebRequest)
           req.Referer = https://passport.baidu.com/?login
          req.ContentType = "application/x-www-form-urlencoded"
        req.AllowAutoRedirect = True
        req.Timeout = 20000
        Dim postData() As Byte
        postData = Encoding.GetEncoding("GB2312").GetBytes("tpl_ok=&next_target=&tpl=mn&skip_ok=&aid=&need_pay=&need_coin=&pay_method=&u=http://baidu.com&return_method=get&more_param=&return_type=&psp_tt=0&password=******&safeflg=0&username=********&verifycode=")
        req.ContentLength = postData.Length
        req.CookieContainer = cc

        req.Method = "POST"
        Dim sm As Stream = req.GetRequestStream

        sm.Write(postData, 0, postData.Length)

        Dim strResult As String
        Dim res As HttpWebResponse = CType(req.GetResponse, HttpWebResponse)

        res.Cookies = cc.GetCookies(req.RequestUri)
     
            Dim smRes As Stream = res.GetResponseStream

            Dim sr As New StreamReader(smRes, Encoding.GetEncoding("GB2312"))

            strResult = sr.ReadToEnd()

            res.Close()
            WebBrowser1.DocumentText = strResult