I've had a few folks ask me about the XML format from Word 2003, and whether or not it would be supported in Word 2007. I mentioned this back in the fall, but in case you missed it let me repeat that the Word 2003 format will continue to be supported in Word 2007.
There are a ton of folks out there who have already built solutions on top of the Word 2003 XML format, and those will continue to work. Everyone can decide for themselves whether they want to port those solutions forward into the new Open XML format, or keep them in the 2003 XML format. The new Open XML format is largely based on the Word 2003 XML format, so you'll see a lot of similarities.
One of the benefits of the Open XML format over the Word 2003 format is the number of Office versions that will support it. As you all know by now, the new Open XML formats will work in Office 2000, XP, 2003, and 2007; while the Word 2003 XML format will work in Word 2003, and 2007.
The XML formats in Word 2007 will be:
We also will continue to support opening anyone else's XML files as well, just like we did in Word 2003. Here's an entry I made back in the summer about opening your own XML files in Word: http://blogs.msdn.com/brian_jones/archive/2005/08/16/452478.aspx