Tosca,
I meant to say that - in practice - most if not all of the text (including tables and formatting) will be the same in an higher version of Word. I never have any problems reading Word XP documents in Word 2000 (or vice versa) nor with reading Word documents my students send me (and a lot will be using Word 2003 by now) in my Word 2000.
Different printers, different printer drivers, different OS'es, different versions of fonts may result in minor changes in the lay-out, like a last line of a page going to the next page, or maybe pictures moving a little bit around. But those changes would result also when using the exact same version of Word.
When sending a Word document for editing, those changes generally aren't important. When sending it for reading only, it's better to send it as a pdf-file. A pdf-file looks the same everywhere (and it's smaller, generally).
My students have to deliver the final versions of their documents in print, so they and they alone are responsible for how it looks. And sometimes that goes wrong: printing complex figures on a laser printer with not enough memory results in a corrupted print (better use inkjet then).
For drafts I don't mind the details.
So it depends on what the receiver does with the document.
Hope this helps.
Kees