What the US wants is Musharaff as the President and Benazir as the PM. To achieve this objective, Musharraf will allow PPP to be the single largest party but just by a wafer thin margin. In order to be the PM, she will have to draw support from the parties loyal to Musharraf. Nawaz Sharif, Imran Khans' parties will be completely routed and they would be left with no leverage in the national politics. Benazir will become PM but Musharraf will remain in total control as Benazir will remain fully dependent on the supporting parties to remain in power.
This honeymoon will last for a while before a disgruntled Benazir tries to get powerful somehow. By this time, the initial euphoria over PPP victory would have died down and the Paki people will realise that there has been no improvement in the governence and the poll promises have not been fulfilled! The support for PPP will gradually erode and antiincumbancy factor will play its part. Finally, a year or so after the election, Benazir would have lost her popularity and Musharraf will reign supreme!