Actually, most of RPGCode, even in the early days (oh how I miss them) took most of its elements from C. With the changeover to the newer RPGCode, it's more reminiscent of C++.
3D Programming is a difficult task, when you're just starting out. Forget about C, C++ is the preferred language today. Grab a book, look up tutorials, take a few classes. Learn the basics and core programming elements in C++ first, then move on to more advanced C++. After that, then you can start looking into Direct3D, OpenGL, and *cough*WinGDI*cough* -- not to mention WinAPI for general Windows programming. There's also a major portability factor for C++. Assuming you don't use too many proprietary libraries (such as the windows.h header file, or directx) it's not a major problem to port C++ code to other operating systems. Despite being more difficult, I'd suggest OpenGL as your 3D API of choice, as it's cross-platform.