Something to help you get a good nights sleep - she's Third in line to the Presidency...its in the Constitution!!
Something to help you get a grip on the Constitution. If Cheney steps down Bush nominates a new VP and the congress approves (or not). The nomination of Pelosi would be about as likely as a space alien walking through my door right now.
But both the president and V.P. have to both die/leave their offices at the same time, for the Speaker of the House to become president.