Quite often projects requirements for a business app include exporting to or importing from MS Excel. There are a few ways of doing this. The most powerful is using automation with Excel Object Model. Other alternatives include OLE DB Access, Comma separated files and XML (there is a nice quote: "XML is like violence: if it doesn't solve your problem, you aren't using enough of it".
In my current project I am using OLE DB Access method. Trust me, you have to be cautious when deciding to adopt it. It has quite many limitations and quirks, that you are probably not expecting. For reference look at How To Use ADO with Excel Data from Visual Basic or VBA. Read this very carefully and follow the links in the end to get a detailed picture. I learned through experimentations a lot of things about accessing Excel through OLE DB, but probably it was a better idea to read this article in depth first.
The problem is that Excel Automation is also not easy to do. First you have to understand a complex object model. Then if you are using it through .NET you must not forget to employ the MS Office PIA and to be aware that if you are in a non "en-US" thread than many of the calls just fail with an ugly error. There can be also some performance issues if you are not doing things right...
OK, I have to stop weeping and get back to work (and do some more miracles with Excel)