I sat down with the AdventureWorks2000 Business Data Catalog (BDC) sample for Microsoft Office SharePoint 2007 recently. Before I launched into it, my big question was, What is the BDC?
In SharePoint 2003, it was possible to display data from an external source, such as your company's database or web services, in SharePoint. Write a custom web part, have it query the data source, and display the data. The big difference with the BDC in 2007 is that this data can now be fully integrated throughout SharePoint, just like Active Directory data. You can search on it using SharePoint's search engine, you can expose it via web parts shipped with SharePoint, or you can write your own to do entirely new things with it. No longer is the data stranded on a web part island.
By the way, setting up a BDC connection is no trivial endeavor. You must write a complex XML document which maps the data in your data source, as well as the method you use to connect, so SharePoint knows what to do with it. Once it's done, though, the BDC gives your portal a pretty powerful way to show people what's going on, right now, inside your company's systems.
To get started with the BDC, I worked through the AdventureWorks2000 Sample on MSDN. Todd Baginski has a nice SharePoint blog and has created a tool for generating BDC metadata automatically. I haven't used it but it might save you some time.