Private Sub TextBox_PreviewKeyDown(ByVal sender As System.Object, ByVal e As _
  System.Windows.Input.KeyEventArgs)
  Select Case e.Key
    Case Key.D0, Key.D1, Key.D2, Key.D3, Key.D4, Key.D5, Key.D6, Key.D7, _
      Key.D8, Key.D9
  Case Else
    e.Handled = True
  End Select
End Sub

Ralf