Ummm I don't really think that you can keep the memories active in your brain once your reborn. Becuase as a baby the brain is to small to hold all the knowledge that you know when you died last. So I think that once your older then I guess through medetation and hypnosis (Did I spell those wrong?) that you can re-gain your past life's memories...
reincarnation is believed to be a cycle system put in place to ensure we learn important lessons. the thought in buddist cultures is that once you reach a level of spirituality beyond divine, your souls breaks free from the cycle and moves on to the etheric. (the term buddah is given to all souls that reach this level.)
You wouldn't forget your past life because of brain size as a baby, the theory of memory relying on brain size was disproven many decades ago. There are two possibilities as to why we don't remember our past lives: 1 is that it never happened and heaven is real as well as hell, the other possibility is that we're not supposed to remember them in our brain's memory because those memories are in the soul. If you think about it the brain remembers and responds to things that effect your current shell, the soul is the ONLY thing you still have from your past life and thus the soul would be where those memories are.
I believe in both theories, personally. I think there is a heaven and hell for people who don't want to be reincarnated, aren't supposed to be reincarnated, or for people who have served their time in this dimension. If the soul can retain memory then you should be able to access it through meditation or, against my advice, through hypnosis. You can't, however, set something up so that in your next life you will be born with the memories of your current life because in your next life (unless you are some kind of science experiment that happened to have the brain of your current shell) you will have a new brain which will hold new memories that will be for your new shell.
I agree with Ragnorok, except, I think that everyone can be reincarnated, just not everyone is ready to when they pass on. Heaven and Hell are places to prepeare you for your next life. I also think that if you were evil in your lifetime then in your next life you will become something "less" than what you were because that will teach you a lesson, and if you were truly pure and good then you would become something "more" as a reward. But you can take a "break" from life in Heaven and you learn your lessons if you were truly bad in Hell.