Well, in all fairness, the FAQ does say
Information about the number of posts associated with member status can be found in the "Help" section. In addition to the status that occurs automatically based on post count, you will find another called "Elite". In this case, it is not based on number of posts but rather is granted by the forum Administrators based on input from the forum Moderators.
However, I couldn't find any reference to the various ranks in the help.
Searching for the word "rank" doesn't get any hits.
Anyway, I think it goes like this(correct me if I'm wrong):
Junior Member - 1-199 posts
Member - 200-999
Golden Member - 1000-1999
Platinum Member - 2000-2999
Diamond Member - 3000-9999
Lifer - 10000+
[edit] Quakefiends post is probably right on more counts than mine, but I do know there's a Platinum somewhere in there. [/edit]