Awesome pics everyone!
Really like your nebula Kill, subtle colors, real nice.
@Phoenix - I too have some personal nebula backgrounds I created that I haven't released in a pack. However, the current pack that Kill and I recently released has a wide selection of many of the ones that we have in our personal installs. In the readme for the pack, I give instructions on how to substitute different .tga's to interchange with other images as backgrounds in any given install. Unless you have Photoshop or some other image editing software where you can view each of the original .tga's that came with BC and then can replace them with the new ones in my pack, you will not be able to "view" each image to see what it is being replaced with - thereby knowing which system background it replaces.
I know the location of the different system scripts is in Scripts -> Systems. If you open each of the .py's using Notepad for individual systems, there will be an entry as to what .tga background is being used for any given system. But once again, unless you have an imaging program to view those .tga's (there are free image editing apps available online such as GIMP), you'll have to "view" each .tga the slow way... that is: launching the game, going to a particular system and looking around a bit until you see the background. Then, taking note of what that background looks like and corresponding it to its name and then quitting BC, going back to your desktop and finally, replace the aforementioned .tga you just viewed in-game with one of the new ones in the pack.