Does anyone know if lucas got james earl jones to do the voice of vader in ep 3? and are we going to see luke skywalker and princess leia?

Don't know about the James Earl Jones question but as far as Luke and Leia, we will probably see them as babies.

Yes, James Earl Jones will be in Star Wars: Revenge of the Sith.

Possibly spoiler....










Ive read that the last few minutes of the film will be Luke and Leia (as babies) being dropped off to their new guardians, while the final shot is Vader with the Emperor looking out from the Death Star.