Private Sub ButzurückClick(sender As System.Object, e As System.EventArgs)
  If DataGrid1.CurrentRowIndex  > 0 Then DataGrid1.CurrentRowIndex -= 1
End Sub

 
Private Sub ButweiterClick(sender As System.Object, e As System.EventArgs)
  Dim dv as DataView = CType( DataGrid1.DataSource, DataView)
  If DataGrid1.CurrentRowIndex < dv.Count-1 Then DataGrid1.CurrentRowIndex += 1
End Sub