If you're interested in seeing the presentation I gave at PDC back in September, it's now available online: http://microsoft.sitestream.com/PDC05/OFF/OFF304.htm#nopreload=1&autostart=1
It's about an hour and 15 mins. It's pretty much a developer level introduction to the Office '12' file formats. I show a number of demos and cover the following agenda:
If you get a chance, please take a look. It really should help you understand more about the formats and how you can work with them.