thanks all for your help,
here is the cod ei added
Sub MyDataGrid_ItemCreated(Sender As Object, e As DataGridItemEventArgs)

        Select Case e.Item.ItemType
            Case ListItemType.Item, ListItemType.AlternatingItem, ListItemType.EditItem
        Dim myTableCell As TableCell
        myTableCell = e.Item.Cells(0)
            Dim myDeleteButton As Button
            myDeleteButton = myTableCell.Controls(0)
             myDeleteButton.Attributes.Add("OnClick","button=th is.value")

        End Select

    End Sub




then i added this to the datagrid:
OnItemCreated="MyDataGrid_ItemCreated"