Sub Form_Load([..])
For Each obj As Control In Me.Controls
            If TypeOf (obj) Is TextBox Then
                AddHandler CType(obj, TextBox).TextChanged, AddressOf _
                  MyTextBoxes_TextChanged
            End If
        Next
End Sub
Private Sub MyTextBoxes_TextChanged(ByVal sender As Object, ByVal e As _
  System.EventArgs)
        ' hier deine Ereignissbearbeitung aller TextBoxen
End Sub