Public Class NumericTextBox
   Inherits TextBox
 
   Public Sub New()
       MyBase.New()
   End Sub
 
   Protected Overrides Sub OnKeyPress(ByVal e As KeyPressEventArgs)
      MyBase.OnKeyPress(e)
 
      Select Case Asc(e.KeyChar)
         Case 48 To 57, 8, 32, 44
            ' Zahlen, Backspace und Space zulassen
         Case Else
            ' alle anderen Eingaben unterdrücken
            e.Handled = True
      End Select
      If CType(sender, TextBox).Text.IndexOf(",") <> -1 AndAlso e.KeyChar = _
        "," Then
         ' Nur ein Komma zulassen
          e.Handled = True
      End If
   End Sub
End Class

Ralf