Ridely stated that the movie is in the same universe as Alien and it provides an origin story to how the Aliens ended up on the derelect craft from the original Alien (Remember the Space Jockey?). He also said that however, you will not be seeing a xenomorph (name of the original alien) in Prometheus.
I really hope that the studio decides to go hard R in this movie. I’m so sick of these pansy ass PG-13 horror/sci-fi movies that try to keep the rating down to market to a larger audience and in turn make more money.
Growing up I was absolutely obsessed with the Alien and Predator Franchises, and to be frank - both franchises have sucked massive dick as of late (I was so/so on the Predators reboot that came out last Summer).