We've worked on this using Word styles and a heap of macros which
allow us to "export" remapping the styles to markup. Basically you
figure out what markup you'd like applied and then what WYSIWYG style
you would like the user to apply (ie work in) then on export the
styles are all remapped to XML tagging.
The beauty of this is that you can tag as much as you want - the
tagging is all done behind 'formatting' which from the user point of
view is just fine. They don't have to know about XML, just about which
styles to apply where in a Word document. And you can also export/hack
the stylesheet to be CSS if you are really going for it then you have
the markup and the formatting instructions separately.
If you want to know more specifics, mail me privately.
Baden