ok yerssot,
You may have changed my mind.
On the star wars site it does talk about leia:
"Leia has few memories of her true mother, Padmé Amidala. All that Leia can recall is that she was beautiful, but sad."
It also says:
"She was one of a set of twins, born in secrecy and protected from Vader and the Emperor. The Jedi hero and general, Obi-Wan Kenobi, secretly transported Leia and her mother to the planet Alderaan, where she was to be raised by Kenobi's friend Bail Organa."
It sounds like this is after Anakin has already become Vader so we might not see the twins in Ep. III.
But with Lucas you never know because it also sounds like Vader never knew they were born - " born in secrecy and protected from Vader and the Emperor" - so who knows. Guess we will find out in 2005