I just discovered a curious thing.
If you rename an OpenOffice.org file to a .zip file, you can unzip it and read its innards in plain XML.
It doesn’t work like that in Microsoft Office 2003, but it should be the default in Office 2007 – except the actual XML will look completely different. To make things utterly confusing, Microsoft called their kind of XML “Office Open XML”. Get it? “Office Open”, but it is not compatible with Open Office.