想下载文件的部分字节，为什么request.AddRange()不起作用？

我想从文件中读取一部分字节，可是不知为什么总是读取了整个文件，请各位赐教：
 原文件大小：3452字节
 程序如下：
 
         Dim totalBytes As Integer = 0
         Dim fs1 As New FileStream(Path.GetFileNameWithoutExtension("test") + ".$$", FileMode.Create)
         Try
             Dim rqs As HttpWebRequest
             rqs = CType(HttpWebRequest.Create("http://.../templates/jtjy/skins/default/images/jy_01.gif"), HttpWebRequest)
             rqs.AddRange(0, 2452)
             Dim strm As Stream
             strm = rqs.GetResponse.GetResponseStream
             Dim receiveBytes(512 - 1) As Byte
             Dim readBytes As Integer
             readBytes = strm.Read(receiveBytes, 0, receiveBytes.Length)
             Do While readBytes > 0
                 fs1.Write(receiveBytes, 0, readBytes)
                 totalBytes += readBytes
                 readBytes = strm.Read(receiveBytes, 0, receiveBytes.Length)
             Loop
             strm.Close()
         Catch ex As Exception
             MsgBox(ex.Message)
         End Try