Are you asking about Project 2003 Standard and Professional desktop
applications or the Project Server 2003 server application?
If you're talking about the desktop PM application, support for the
Workgroup Tools that sent task assignments, etc, via email that was in
earlier versions has been withdrawn in the current release. It can be
re-activated by following the directions in an article in the MS support
Knowledgebase, article number 818337 and that also discusses the system
requirements. It does require the email system to be fully MAPI compatible
and to the best of my knowledge Groupwise is not. I'm pretty sure the only
system supported besides Exchange is Lotus Notes and even Notes often proves
iffy in practice.
HTH