Private Sub TextBoxen_KeyPress(ByVal sender As Object, _
  ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles Text_1.KeyPress, _
  Text_2.KeyPress, Text_3.KeyPress, Text_4.KeyPress, _
  ComboBox_1.KeyPress, Text_5.KeyPress
 
        With Text_1
            Select Case Asc(e.KeyChar)
                Case 44, 46 ' Komma, Punkt
                    If InStr(.Text, ",") < 1 Then
                        ' nur falls noch kein Dezimalzeichen vorhanden
                        If .TextLength = 0 Or .SelectionLength = .TextLength _
                          Then
                            If .SelectionLength > 0 Then .Text = ""
                            .AppendText("0,")
                            e.Handled = True
                        End If
                    Else
                        e.Handled = True
                    End If
 
                Case 48 To 57, 8
                    ' Zahlen, Backspace und zulassen
 
                Case Else
                    ' alle anderen Eingaben unterdrücken
                    e.Handled = True
            End Select
        End With
    End Sub