Hakan,
I will answer both questions here.
First, if an entire project is delegated to an owner, and hence GRO is personal organizer handling your own projects and activities, then for you this is not a project but rather one activity to "follow-up project X". And here you can assign a contact, in this case owner.
Second, you can assign sub-activities - just stand on an activity and press "New". Sometimes thts may be justified, but as a rule, it is more apt to define anything consisting of multiple activities as project (also in accordance with GTD methodology).
Michael.
