Private Sub TextBox1_KeyPress(ByVal sender As Object, ByVal e As _
  System.Windows.Forms.KeyPressEventArgs) Handles TextBox1.KeyPress
        Select Case Asc(e.KeyChar)
            Case 48 To 57, 8              ' nur Zahlen und Backspace 
            Case Else
                e.Handled = True          ' alle anderen Eingaben unterdrücken
        End Select
End Sub