Usando Timers em VB.NET (Windows Forms)

Private Sub Timer1_Tick(ByVal sender As System.Object, _
     ByVal e As System.EventArgs) Handles Timer1.Tick
  'acrescenta um "X" na barra de títulos a cada
  'disparo do timer
  Me.Text = Me.Text & " X "
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, _
     ByVal e As System.EventArgs) Handles Button1.Click
  'inicia o timer
  Timer1.Start()
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles Button2.Click
  'pára o timer
  Timer1.Stop()
End Sub