Ted,

I hope you realize that your class can create a StreamWriter or a
BinaryWriter based on the plain IO.Stream variables. In fact a BinaryWriter
needs a previously open IO.Stream in order to use it. A StreamWriter can
accept either a file name or a Io.Stream in its constructor.

Which is part of the beauty of the System.IO namespace and having the
IO.Stream independent of the BinaryWriter & StreamWriter classes. The
writers are not tied to a specific stream & the stream is not tied to a
specific writer!

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlr
fSystemIOBinaryWriterClassctorTopic2.asp

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlr
fSystemIOStreamWriterClassctorTopic1.asp

The trick is making sure that you only flush the writer without closing the
underlying Stream.

Something like:
   Public Sub Main()
       Dim stream As New FileStream("myfile.txt", FileMode.Create)
       Line1(stream)
       Line2(stream)
       stream.Close()
   End Sub

   Public Sub Line1(ByVal stream As Stream)
       Dim writer As New StreamWriter(stream)
       writer.WriteLine("This is the first line")
       writer.Flush()
   End Sub

   Public Sub Line2(ByVal stream As Stream)
       Dim writer As New StreamWriter(stream)
       writer.WriteLine("This is the second line")
       writer.Flush()
   End Sub

What I'm not sure is how calling StreamWriter.Flush relates to the
underlying Encoding object associated with the StreamWriter. Based on the
help for StreamWriter.Flush.

Hope this helps
Jay