I started asking about CrystalSpace 3d over at GameDev.net, and someone said that it's a great renderer, but only with CrystalCore does it become a true 'engine' for me to use. I'm intending to make an RTS in the future using your engine, and was wondering how I make use of CrystalCore? I downloaded the CrystalSpace into, compiled the walking demo, and have read into some of the manual. Is CC another package I need to download, or what?
That is wrong. Crystal Core is not a game. It doesn't make CS a game engine. If you want to use a full game engine then you should use Crystal Space and Crystal Entity Layer (or CELstart). Both together form a full game engine.
So just download Crystal Space (as you already did) and then Crystal Entity Layer.