How do I change camera targets when following a path? I have a nurbs path setup and my camera operates following the path. I can get it to track an empty, but I want it to change between a couple of empties as it progresses down the path. 

Is there a way to do this using the timeline?
You don't "change" camera targets, but you can have several Track-To constraints in the same object with different influence values at any given time.

Just keyframe the Influence parameter over the course of the animation so it points where you want at the correct moment.