Just stumbled across an article by Sharepoint MVP Rehman Gul which gives a short guide on adding MSCRM functionality into your MOSS 2007 site.
This guide is useful for giving you an idea on how the Business Data Catalog works.
On a side note, I don’t know how many of you used MSCRM before v3, but if you did you’d have one hell of a wicked bad taste in your mouth. You probably aren’t using it anymore, or won’t use it again. But, before you give up on it, give v3 a shot. It’s prettier, less painful to manage, and it doesn’t plant itself in your Active Directory anymore. And you get awesome cross-app functionality.