There are a number of great sources of information on the new Office Open XML formats out there. I like to think that this blog is one of those sources, but there is also the OpenXMLDeveloper.org community, and the Ecma TC45 site. Another great source of information though that I always forget to mention is actually the official MSDN site for Office XML development: http://msdn.microsoft.com/office/tool/xml/default.aspx
There is a lot of good content up there, and it will continue to grow as we move closer to RTM. One article that you guys might want to check out is: “Walkthrough: Word 2007 XML Format” written by Erika Ehrli. It shows you how to build your own WordprocessingML document from scratch, as well as provides an overview of things like the Open Packaging Conventions (parts, relationships, content types), and the custom XML data store.