The evil thing about Blue Marble,a s far as I can see, is that it doesn't follow the standard modding directories, but simply replaces C-IVs terrrain graphics with new ones (made from the NASA Blue Marble Project Satelite Photos).
Even worse, I don't know how to make it affect only one folder, since the install script looks for the places it needs to install on its own, without the option to unselect parts. The way it works is: DL the file, start the script, chose detailed or simple terrain, it tells you which files will be replaced, it replaces them (for both C-IV and Warlords), next time you start (or maybe after a reboot, I'm not sure) you've got slightly more realistic graphics for terrain.
By the way, now that I've reinstalled C-IV, it seems my language is reset to German. Not the text, you can change that, but the sound. Guess it's time for another reinstall... *sigh*
Edit: to check out Blue Marble screenshots, look for it on the Civfanatics home page