I've tried this:
    'start Excel app
    Dim exApp As Microsoft.Office.Interop.Excel.Application
    exApp = CreateObject("Excel.Application")
    ' load excel document
    exApp.Workbooks.Open(fname)
    Dim exSheet As Microsoft.Office.Interop.Excel.Worksheet
    exSheet = exApp.Workbooks(1).Worksheets(1)
and than, for example accessing "C3" cell:
 Dim b As String
 b = exSheet.Cells("A3")
or:
b = exSheet.Cells(3,3)
and it throws me an exception. I'm feeling that I'm doing something wrong with the object access, but this method worked in embedded VB, and do not works in .net. Also, tried to google the exception code, with no relevant result.