Sounds like you have 2 questions with the assumption being that you're
talking about Outlook on your personal computer

First - how to get data out of Groupwise into a format which can be imported
by Outlook - this may be what you need:

Export Address Book Group Members to CSV
http://www.novell.com/coolsolutions/tools/1684.html
*** caveat - the standard Outlook import function will not import any custom
field information if you have any

Second - syncing via a common field between the two

Outlook has no import capability to import based on a common key - you'd
need to write your own code or use a 3rd party product for that (such as
ContactGenie DataPorter - if you're only looking for one way data movement -
reverse updating won't be available until the release of the ContactGenie
2.1 series). In any event, you have to determine which field (or group of
fields) would uniquely identify a contact between the two which could be
either any standard or custom field combination (in terms of CGD).

You may also find other potential solutions to your requirement here:
http://www.slipstick.com/addins/contacts.htm (there are other pages on
Slipstick which may have other applicable alternatives)

Karl