Thanks Mike, but, just to make sure I understand what you mean... that I should create multiple space images, and then map them onto multiple layered semi-transparent spheres? This would give my background some depth for moving camera shots.

I think I'll still run into problems with planets though. As in, they should be entirely non-transparent, with no stars in front of them, and nothing viewable through them of course.
If I put them on the backmost layer with no transparency, there's still a problem that a star could end up in front.