In the words of our Head Web Guru (Mike Loffland) -
Basically.... the "live" forums only contain THREADS that were started on or after 1/1/2008... there is now a "Forums Archive" link where our users can access threads started before 1/1/2008. The "Forums Archive" only allows searching and browsing... you cannot login, respond, or start new threads.
If you have any questions about this process, feel free to ask a moderator or administrator - or post a question in the Feedback forum.
Best regards and clear skies!