I have yet to find a clean way to import old Outlook mail files to the Mac environment. There are some for-sale utilities out there that purport to do so but the demos that they have of them mashed up my Email files so I'm leery about the whole process. As of now, my old Outlook emails remain in Outlook in a virtual Windows environment on my Mac (finding that I don't really need to look at them very often).
Masaki