I've heard of Weiss and have seen the book. It's nothing I haven't come across before - it's interesting stuff. I wouldn't put much stock in this being tantamount to Scientology teachings. You might want to read Journey of Souls, by Michael Newton to further explore the idea of souls and what they do between lives.
From Amazon:
Journey of Souls is a controversial yet inspiring investigation of the big question we all face at one point or another: "What happens after we die?" To find the answer, Newton opens cases from his private practice in which he hypnotically regressed his clients to a point between lives--after death, but before birth. Not only does Newton grapple with reincarnation, the spirit world, and the nature of the human soul, he also tackles equally sticky questions such as "Is there a Heaven and Hell?" and "What are ghosts?" Readers with a penchant for skepticism will balk at the lack of physical evidence to back up the claims in Journey of Souls, but the book remains a reassuring voice, affirming that our existence is not limited to the boundaries of our mortal flesh. --Brian Patterson