I am working on this. I have several vehicles skinned and ready, and many terrains to drive, but I need to finish the logic with a way to keep the score game to game. Feedback is welcome.
Just unzip it to your C drive. Make sure you have the dependencies 3D RAD needs. It should play with no trouble.
This video uses software to quickly and easily make a 3D mesh - Terrain and then install it in 3D RAD. List of software and explanations of work done.