Long pressed button

UPDATED: Shortest way:

Using Anonymous Methods and Object Initializer:

public void Repeater(Button btn, int interval)
{
    var timer = new Timer {Interval = interval};
    timer.Tick += (sender, e) => DoProgress();
    btn.MouseDown += (sender, e) => timer.Start();
    btn.MouseUp += (sender, e) => timer.Stop();
    btn.Disposed += (sender, e) =>
                        {
                            timer.Stop();
                            timer.Dispose();
                        };
}