Whatever is after P.P., how mant posts do you have to make to become that?
Devious Doorman- 500+
is the next one
however it doesn't change automatically, you must go to the advancements thread in Alarming Announcements and ask to be raised a rank and the lovely swans will take care of that for you that applies to all of the rank advancements from Devious Doorman and upwards
By being an important moderator, probably along with some other condition. Very few of us will ever be able to access that board, although we have been informed that the Ruefully Restricted boards are actually not very interesting.
Just a starter answer while you wait for someone like swans to arrive and give us a more detailed explanation, since she actually knows, I assume.