Let's see, you asked a question about Word running on Windows Vista in a
newsgroup for general questions about Windows XP. Don't you think you
might have tried to find a Word newsgroup or even a Vista newsgroup?
microsoft.public.word.docmanagement
microsoft.public.windows.vista.general
Or you could always try the good old MSKB search tool:
http://support.microsoft.com/search/
...which gives this answer:
"Information about using 2007 Office suites and programs on a computer
that is running another version of Office"
http://support.microsoft.com/kb/928091/