Dim wb As Excel.Workbook = _
  CType(GetObject("F:\daten\mappe1.xls"), Excel.Workbook)
 
  Dim exapp As Excel.Application = wb.Application
 
  Dim xlblt As Excel.Worksheet = _
  CType(wb.Worksheets("Tabelle1"), Excel.Worksheet)
 
  Dim rg As Excel.Range = CType(xlblt.Cells(1, 1), Excel.Range)
 
  Dim content1 As String = CType(rg.Value, String)
  rg.Value = "1234"