Thanks. Is it possible to key parents, so that say a camera is pointing at a car for one part of an animation, then it swings to point at a different car?

Incidentally I also found my problem with aim constraint, which I will put here in case anyone else has it and finds this in a search. It seems the constrained axis was 1,0,0, but normally the light points along the z-axist, and not the x, axis, so to get the light to point at something that you constrain it's aim to, change the constrained axis to 0,0,-1