There seems to be some confused people on this thread.
Let me state definitively that the 40/20 rule was first used in the 1997 ARL Competition.
It was not part of Super League's competition at any stage. I am as certain of this as I am that Newcastle and Brisbane won their respective competitions that year.
As some have pointed out earlier, Super League introduced the 0 Tackle rule which at that time applied to kicks as well. Both rules were trying to adress the problem of fullbacks and wingers dancing along the sideline waiting for the ball to go over so a scrum could pack.
In 1998 when the two comps got back together the ARL's 40/20 rule was adopted as was a modified version of the 0 tackle rule ie. it no longer applied to kicks, but only to handling errors.
Cheers.