Does Crystal Space use Direct3D?
No, Crystal Space works with OpenGL (or software rendering) on all platforms.
Do I need a C++ compiler to use Crystal Space?
Yes and no. To use the basic Crystal Space and Crystal Entity Layer source packages you need a C++ compiler. You will also need a C++ compiler to compile your own project sources. However, you can also use CELstart which is a precompiled application that contains Crystal Space and Crystal Entity Layer. And using CELstart you can make applications with Python or XML without the need for a C++ compiler.