Hiya Bucko !
RMAD (if you can attend one) is a very worth while session to go through. It will give you a very good indication of how you stand fitness wise and highlight any areas that need work prior to going to PRMC. It will also give you a rough idea of what is expected of you as well.
RMAD is made up of several tests from prmc - day 1 of prmc (3miler, 2mins press ups, sit ups & max pull ups) then something similar to gym test 2 on day 2 of PRMC.
There have been a lot of guys on the site who have attended, they should be able to give you more indepth idea of what else goes on.
Hope that helps,
Shiloh.