Reading/Writing Excel Spreadsheets with ADO.NET
David Hayden maintains a really great blog. He regularly posts about ADO.NET and Data Access, and is someone I'd highly recommend subscribing to.
He posted a useful blog entry a few days ago that details how to use ADO.NET to read, insert and update data from an Excel spreadsheet. A useful read if you are looking to quickly export or import data and work with it interatively in Excel.
Hope this helps,
Scott