How to make an parallax starfield background

I want to make an parallax starfield background for my 2d game. I want to be something like the starfield in this flash game: Play FlashTrek, and more RPG Games! | Max Games
My game is in 2D and i’m using an orthographic camera which I will probably need to switch to perspective.
So how do I go about doing this?
thanks in advance

Bit of an old thread and I am shamelessly pushing our own work but if you willing to part with $2.5 to $10 you can check out our backgrounds with built in parrallax effects:

Otherwise its really simple. All you really need to do is use a perspective camera (to give depth) and place your sprites at different distances from the camera. Then as your camera moves/zooms you will see a nice parrallax effect.

This looks like a pretty good tutorial on how to achieve the effect – without switching your camera to perspective. The short answer is that you manually scroll the farthest away elements at a rate that is slower than the elements closest to the camera. See the link for the details.