配列のポインタ操作

byte[] buf = new byte[1024];
MemoryStream ms = new MemoryStream();

while (受信完了まで) {
  int ret = soc.Reacive(buf);
  ms.Write(buf,0,ret);
}

Bitmap bm = new Bitmap(ms);

//以降、ビットマップクラスを利用する処理

//ソケットの代わり
FileStream fs = new FileStream(@"TEST.bmp",FileMode.Open);
byte[] buf = new byte[1024];

MemoryStream ms = new MemoryStream();
while(true){
   //次のREADはソケット受信の代替
   int cnt = fs.Read(buf,0,buf.Length);
   ms.Write(buf,0,cnt);
   if (buf.Length > cnt)break;
}
fs.Close();
Bitmap bm = new Bitmap(ms);
pictureBox1.Image = bm;
pictureBox1.Update();

class BmpServer
{
    [STAThread]
    static void Main(string[] args)
    {
        try
        {
            int p = 13000;
            IPAddress ip = IPAddress.Parse("127.0.0.1");
            TcpListener sv = new TcpListener(ip,p);
            sv.Start();
            try
            {
                Console.Write("接続待ち");
                TcpClient cl = sv.AcceptTcpClient();            
                NetworkStream ns = cl.GetStream();
                Console.WriteLine("接続中");

                using(FileStream fs = new FileStream(@"E:\Data\TEST.bmp",FileMode.Open))
                {
                    byte[] data = new byte[fs.Length];
                    fs.Read(data,0,data.Length);
                    ns.Write(data,0,data.Length);
                    ns.Flush();
                }
                cl.Close();
            }
            finally
            {
                sv.Stop();
            }
        }
        catch(SocketException e)
        {
            Console.WriteLine(e.Message);
        }
        Console.WriteLine("終了します");
        Console.Read();
    }
}

private void button1_Click(object sender, System.EventArgs e)
{
    IPAddress ip = IPAddress.Parse("127.0.0.1");
    IPEndPoint iep = new IPEndPoint(ip,13000);
    Socket s = new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
    s.Connect(iep);
    if (!s.Connected)
    {
        MessageBox.Show("接続失敗");
        return;
    }
    byte[] b = new byte[1024];
    NetworkStream ns = new NetworkStream(s);
    MemoryStream ms = new MemoryStream();
    while (ns.DataAvailable)
    {
        int ret = ns.Read(b,0,b.Length);      
        ms.Write(b,0,ret);
    }
    Bitmap bmp = new Bitmap(ms);
    pictureBox1.Image = bmp;
    pictureBox1.Update();
}