C#

Hide();
bool done = false;
ThreadPool.QueueUserWorkItem(
    (x) =>
    {
        using (formSplash = new FormSplash())
        {
            formSplash.Show();
            while (!done)
                Application.DoEvents();
            formSplash.Close();
        }
    });
// Do stuff...
done = true;
Show();

protected override void OnPaint(PaintEventArgs e)
    {
    using (Pen pen = new Pen(Color.FromKnownColor(KnownColor.InactiveBorder)))
    {
        e.Graphics.DrawRectangle(
            pen,
            new Rectangle(
                Point.Empty, new Size(Width - 1, Height - 1))
                );
    }
    base.OnPaint(e);
}

public class CuelessButton : Button {
  public CuelessButton() {
  }

  protected override bool ShowFocusCues {
    get { return false; }
  }
}

public partial class SplashForm : Form {
  private CuelessButton button1;

  public SplashForm() {
    InitializeComponent();
    this.button1 = new CuelessButton();
    this.button1.Dock = System.Windows.Forms.DockStyle.Fill;
    this.button1.Text = "Please Wait ...";
    this.Controls.Add(this.button1);
  }
}