Basically the system uses a rescource as experience, in this instance stone. When an enemy is killed or quest completed stone is tributed to the player as per the normal method thus representing a gain in experience.
The levels are the hard part, what happens is that a series of looping triggers are set with an accumulate attribute condition. The only problem is that they will continue to add levels. Therefore the trigger must de-activate itself once triggered. Thus stopping continued levels. Other levels repeat the same function with higer accumulated attributes.
At the same time you could implement a name changing and objective changing also to label what level the player was at.
Now I must stress again, that I havnt got this working properly yet. Therefore if anyone can spot any flaws in this strategy and some possible solutions I would be grateful.
Cheers, Morv