Can anyone point to any good 'beginners walkthroughs' for the Business Data Catalog in MOSS 2007 Enterprise? It seems to be very powerful, but all the official guides assume preexisting knowledge.
Have a look at SharePoint 2007 Developer's Guide to Business Data Catalog. The authors (Brett Lonsdale and Nick Swan) have been developing tools and working with the BDC for 'ages' and really know their stuff.
There is an early access available now with the final due to be published in September 2009.