Hey G.T., that's an awesome scenario.
The existing Word 2003 XML format will still be supported in Word 2007. So, if you want to keep generating your reports in that format, you can.
If you want to move into the new Open XML formats, you'll see that the biggest difference is really that we've split the single XML file into multiple parts and wrapping them in a ZIP package (where binary content like images are not longer stored as base-64 encoded text). We'll definitely have a final list of the differences once we get closer to finalizing the Open XML format in Ecma.
-Brian