I thought they actually shared the same Address book, but I have never used
Outlook at all, but knowing Outlook Express & the Window's Address Book
application, as well as I do - and having used the Window's Address Book to
export / import all contacts to things like iTunes, I am fairly sure you will
be able to do what you need to without too much hassle.
Both Outlook and Outlook Express can export and import *.vcf files
(Business Cards), so at the very least, you should be able to export all
your contacts from OE individually, then import them again into MS
Wishing you every success...
Cheers, Tim Meddick, Peckham, London. :-)