Hmmm. This question isn't really about VSTO technology, but about accessing Excel files as databases (in this case, using OLE DB). There are two possible places I can think of to get help on this: the Excel programming newsgroup; the data.oledb newsgroup. You'll also find quite a bit of information about connection strings on Carl Prothmann's site, but I don't know if it goes into this kind of detail for Excel.