openExcel(False) ' ohne text format
   openExcel(True)    ' mit text format
 
   Sub openExcel(ByVal withTextFormat As Boolean)
        Dim ex As New Excel.Application
        With ex
            Dim pfad As String = "foobar.xls"
            .Workbooks.Open(pfad)
            .Visible = True
            .ActiveWorkbook.Sheets("Tabelle1").Select()
            .Range("A3").Select()
            If withTextFormat Then .Selection.NumberFormat = "@" ' hier wird 
            ' das format auf Text gesetzt
            .ActiveCell.FormulaR1C1 = "0000011"
        End With
    End Sub