I have a couple of space scenes in my gallery. In both cases I made a star backdrop in PS and applied it to a 2D square which I positioned and scaled to fill the scene. If you try this, you will probably want to turn off recieve,cast, and self shadows on your background pic. This can work well in a static pic, or even in an animation. I recommend deleting the ground plain. You can also use the starry background sky from Bryce's sky presets, but IMO the stars are not as realistic. Of course, a third way would be to do it in postwork using PS. Orbital wrote a good tutorial about doing just that.