>>642 なんだか駄目ですね。以下コードです。
byte [] hoge = { 1 , 2 , 3 , 4, 5 };
MemoryStream streamA = new MemoryStream( hoge );
MemoryStream streamB = new MemoryStream( hoge );
streamA.Positon = 0 ; streamB.Position = 0;
MemoryStream temp = new MemoryStream();
StreamWriter writer = new StreamWriter( temp );
StreamReader reader = new StreamReader( streamA );
writer.Write( reader.ReadToEnd() );
reader = new StreamReader( streamB );
writer.Write( reader.ReadToEnd() );
Console.WriteLine( temp.Length );