Im reading this book right now by Sylvia Browne called Conversations from the other side. Sylvia is a psychic that has been on the Montel show a lot, Larry King, Unsolved Mysteries. Her reading has also helped solve a few big crimes.
She mentions in her books about these deja-vu experiences. Something about information from our lives before, accidently seeping into our new minds when we are born in a new body.
It's a little deep.
I also saw something on tv about experiences like that, that it had something to do with the electric impulses in the brain.