i'm ready to write my tutorial accurately...
first of all you've to put the attatched "stars.jpg" files into your folder c:/ ....
this is a starfield that i've generated using glitterato (a photoshop plugin, youi may download it for free... it's a limited time demo)http://www.flamingpear.com/download.html
first step, we want to add this starfield to the sky.
Go in the object panel, select your background, than the surface shader tab.
Into this you've to create a new shader, a new "default shader" where now there's a background shader.
Go into it and set the stars.jpg as a background for diffuse colour and for luminosity.
Set the luminosity value at higher value if you want to make stars visible by day.