Public Sub PostTwitterUpdate(ByVal userName As String, ByVal password As _
  String, ByVal updateMessage As String)
    Using wc As New WebClient
        wc.Credentials = New NetworkCredential(userName, password)
        ServicePointManager.Expect100Continue = False
 
        Dim updateMessageBytes = System.Text.Encoding.UTF8.GetBytes("status=" & _
          updateMessage) 'Use UTF8 to get it properly encoded if you use 
        ' characters like ç ã etc...
 
        wc.UploadData("http://twitter.com/statuses/update.xml", _
          updateMessageBytes)
    End Using
End Sub