// Create the server
using (var game = new ExampleGame(new ServerNetworkManager()))
{
    game.Run();
}

// Create the client
using (var game = new ExampleGame(new ClientNetworkManager()))
{
    game.Run();
}

// Network Manager type injected as appropriate.
using (XNAGame game = new XNAGame(new ClientNetworkManager()))
{
    game.Run();
}

// Constructor accepts the "injected" type as below.
public XnaGame(INetworkManager networkManager)
{
    graphics = new GraphicsDeviceManager(this);
    Content.RootDirectory = "Content";

    this.networkManager = networkManager;
}

// RTTI / Polymorphism. Determine if this instance is a Server or a Client.
public bool IsServer()
{
    return this.networkManager is ServerNetworkManager ? true : false;
}

// The Windows form within this project can then be run as follows.
protected override void Initialize()
{
    // TODO: Add your initialization logic here

    // If this is the server, we need to create and show the management form.
    if (this.IsServer() == true)
    {
        Form = new MainServerForm();
        Form.Show();
    }

    base.Initialize();
}