A while back Palin had a question:
McCain (well McCain's staff) must have told her.
In case they didn't here is the answer:
As designated by the Constitution of the United States, the vice president also serves as the President of the Senate, and may break tie votes in that chamber.
That is it as far as official duties. Otherwise it is what ever the President assigns to the Vice President.
By the way I'm still voting for Bob Barr.