Also if you're having a hard time, start with a easier language like VB and not C++

-Just a suggestion

From what i can tell about your level of skill, using and modiflying an existing engine probably is not the best route. If you cannot create a simple game, then there is no way you are going to be able to understand and modify a complex engine. I think the best thing for you to do would be to start with a simple graphcis library, like allegro or sdl. This will allow you to get some results quickly, while still learning a lot more than just using and existing engine.