Brian Jones, Senior Program Manager just broke the news in his post today.
Quoting from him:
"As promised last month, the binary documentation (.doc, .xls, .ppt) is now live. In addition to this, the project to create an open source translator (binary -> Open XML) has now been formed on sourceforge, and the development roadmap has been published. Read my earlier post for more background on this: http://blogs.msdn.com/brian_jones/archive/2008/01/16/mapping-documents-in-the-binary-format-doc-xls-ppt-to-the-open-xml-format.aspx “
Another great surprise in all of this is that we've made the documentation for a few other supporting technologies available as it may be of use to folks implementing the binary formats: http://www.microsoft.com/interop/docs/supportingtechnologies.mspx
The technologies included are: