"Power struggle"?? That's laying it on sensationally thick - typical perspective on an unstable African country from the western press...

Yes, Zuma and Mbeki have been struggling for top-dog position since Mbeki made Zuma his deputy president. It got worse when Mbeki discharged Zuma based on the pretext of Zuma's involvement of the corrupted arms deal - which, to this day, has not been proven in court, because Zuma has made delay tactics a new form of art. It reached fever pitch when Zuma was picked over Mbeki as the party's president.

Yet Mbeki's decision to resign has nothing do with a direct power struggle, but is the fall-out of a historical (and controversial I must add) court's decision in the Zuma trial on September 12. According to the judge, Mbeki intervened in the judiciary system to make sure Zuma got recharged. That's a massive faux-pas for a president. Zuma now wins, because Mbeki and the NPA were too blinded with determination to get rid of Zuma using the courts and made blunders to get their way. The NPA has announced they will appeal the judge's decision, but the damage already has been done.

Obviously AP puts this crucial bit of information on the very end:

The Associated Press: South Africa's Mbeki resigns after power struggle

Although Mbeki's removal came more quickly than many people expected, South Africans had been anticipating a shift from Mbeki to Zuma at least since last December, when Zuma defeated the president in an election for the ANC leadership.

Mbeki fired Zuma as his national deputy president in 2005, after Zuma's financial adviser was convicted of trying to elicit a bribe to deflect investigations into the arms deal.

Initial charges against Zuma were withdrawn, but the chief prosecutor said last December that he had enough evidence to bring new ones. A judge threw out the new charges last week and implied they were the result of political interference.