OK, basically, South Africa's won 4 from 5 (out of 6 total games), and got a bonus point from one of those four wins, giving them 17 points total. New Zealand has won 2 from 4 and has 8 points total. We play South Africa next weekend. If South Africa wins, or even gets a bonus point for losing by less than 7, we're fucked. Series over. Because if South Africa gets to 19 points or more, there is no way we can catch them, and if they are on 18, we need to win BIG to equal that 18 and improve our points differential so that it's better than theirs (currently, ours is -14 while theirs is +25).
BUT, if South Africa ends their six games on 17 points, NZ can still win. If we win both of our two remaining games with bonus points, we end on 18 and win the tournament. If we get bonus points from one, we end on 17 and the aforementioned points differential comes into play. If we don't pick up any bonus points, even if we win both games we just end on 16 and the title goes to the 'Boks.
Complex? A touch!
Oh, and Australia cannot win at all. They can pass NZ if the 'Boks beat us and then they beat us in the last game.