' リクエストの作成
Dim req As HttpWebRequest = CType(WebRequest.Create("http://madoka-run.dyndns.org/upload.cgi"), HttpWebRequest)
req.Method = "POST"
req.ContentType = "application/x-www-form-urlencoded"
req.ContentLength = data.Length
' ポスト・データの書き込み
Dim reqStream As Stream = req.GetRequestStream()
reqStream.Write(data, 0, data.Length)
reqStream.Close()

' レスポンスの取得と読み込み

※恐らくですがここからの処理でエラーが出てます
HTTP/1.1 417 Expectation Failed　となるのが問題らしい？

Dim res As WebResponse = req.GetResponse()
Dim resStream As Stream = res.GetResponseStream()
Dim sr As StreamReader = New StreamReader(resStream, enc)
Dim html As String = sr.ReadToEnd()
sr.Close()
resStream.Close()

おねがいします