Dim re As New System.Text.RegularExpressions.Regex("[a-zA-ZüöäÜÖÄß]")
    Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
        e.Handled = Not re.IsMatch(e.KeyChar)
    End Sub