Meanwhile i've been implementing the Cook-Torrance lighting model, thanks to the articles and help of Jack ( Jollyjeffers on gd.net ). There was a few typos in the equations, but fortunately it didn't took too long to sort out the problems. Unfortunately, i found that tweaking the standard Phong-blinn model gave results looking as good as Cook-Torrance, at a much lower performance cost. The main difference with Phong equations is the addition of the fresnel term, but that's pretty much all..
The first screenshot is a view of the gas giant system from a high distance. Nothing special, but i don't think i posted one like that previously, so here it is.
The two other screens are from the top part of the station with the new shaders ( you don't wanna see the old one: it was really horrible ). I'm still not 100% happy with it, but it's definately an improvement. Some trees should have been visible in the biodome ( top-most part ) but i'm not handling transparent textures yet, so they're hidden.