Also, the game will create NPR races automatically (at random) on habitable worlds when their system is first explored. At this time, you have to then control the race by hand (as Erik says, in 4.0 the computer will control). The frequency of habitable worlds is small, however, so don't be surprised if it takes a LOT (i.e. several 10s) of systems to find one. An SM-mode event will be generated when you enter such a system.
John