// from www.danielmoth.com/Blog/

public enum MyMessageBoxResult
{
  Button1,
  Button2,
  None
}
public static class MyMessageBox
{
  /// <summary>
  /// Displays a message box that contains the specified text, title bar caption, and two response buttons.
  /// </summary>
  /// <param name="messageBoxText">The message to display.</param>
  /// <param name="caption">The title of the message box.</param>
  /// <param name="button1">The title of the first button.</param>
  /// <param name="button2">The title of the second button. Pass null if you only want one button.</param>
  /// <returns>A value that indicates the user's response to the message.</returns>
  public static MyMessageBoxResult Show(string messageBoxText, string caption, string button1, string button2)
  {
    int? returned = null;
    using (var mre = new System.Threading.ManualResetEvent(false))
    {
      string[] buttons;
      if (button2 == null)
        buttons = new string[] { button1 };
      else
        buttons = new string[] { button1, button2 };

      Microsoft.Xna.Framework.GamerServices.Guide.BeginShowMessageBox(
          caption,
          messageBoxText,
          buttons,
          0, // can choose which button has the focus
          Microsoft.Xna.Framework.GamerServices.MessageBoxIcon.None, // can play sounds
          result =>
          {
            returned = Microsoft.Xna.Framework.GamerServices.Guide.EndShowMessageBox(result);
            mre.Set(); // could have done it all without blocking
          }, null);

      mre.WaitOne();
    }

    if (!returned.HasValue)
      return MyMessageBoxResult.None;
    else if (returned == 0)
      return MyMessageBoxResult.Button1;
    else if (returned == 1)
      return MyMessageBoxResult.Button2;
    else
      return MyMessageBoxResult.None;
  }
}