The Box set contains The Arduin Adventure rulebook which includes a beginning scenario, a set of blank treasure cards with illustrations on one side, character sheet, and 1 or 2 d20's. The rulebook is still available from Emperor's Choice. At least that's what my old box set contained.
Arduin Adventure includes fighters, thieves, mages, priests, and foresters as classes. The classes are really simple with only one or two skills/special abilities each. The spell selection is adequate enough to keep a game goign for a while in regard to spell-casters. The game uses a weapon based attack matrix that let's folks hit a fair amount of the time. The monster selection is small but adequate.