Office Business Applications and LOBi
One of the really cool MOSS features is the business data catalog (BDC). The BDC provides line of business search and integration capability via ADO.NET providers and Web services. If you're interested in this, then check out the OBA developer portal and definitely check out the new Line of Business Interoperability (LOBi) technology for MOSS. This newly announced functionality provides a set of services that enables users to access information and processes in line-of-business applications through the familiar environment of Microsoft Office.
For a more general introduction to OBA take a look here: