I found the documentation for the diffgram. I've udated the original post with the location.
This blog is inactive.New blog: EricWhite.com/blogBlog TOC(July 16, 2008: This approach has been replaced with a better version.)
Also, I modified the code that prints the diffgram to remove the extraneous namespace declarations - this cleans up the diffgram significantly.
I've updated the code on the original post. If you downloaded the code from the original post, you may want to get the new version.
I was trying to get OpenXML diff utility, but it requires .NET 1.1. Is the tool updated to work with .NET 2 or later?