There is a check-box "Announcement?" that can be ticked when creating a new thread. Under this check-box, there should be two more options, where two of those are to select in which forums the Announcement would appear in: All Forums? or Select Forums: (Forum List here)
The Announcement(s) would act much like a Sticky, appearing at the top of forums.
The Lock option to disable replies to the thread should also work for Announcements, so the thread poster could choice if he would like to have replies to the announcement or not.