I've been thinking of trying Irrlicht for a while. When I saw how easy it was to integrate Newton with Irrlicht I decided to try it out.
However, you're right. I guess I was giving up on using Newton with DarkGDK out of frustration. After reading you post, I felt guilty, and so I decided to give it another try.
I created a new project, and made the same setup, using a more organized approach. I setup the debug display (hid the DarkGDK objects to make sure I could see everything) and ran the application.
And then I saw something that made everything make sense.
The box that I created for the ground started out in the center of the sceen. The falling box was a little above it. The falling box dropped, and then eventually collided with the ground. Here comes the important part: when the falling box hit the ground, the ground dropped with the box! When I tried before, I was not updating the ground mesh's position with the ground NewtonBody's position, so it appeared that the falling box was passing through the ground.
So I looked over my code. I thought that I read in the Wiki that if you set the mass to below 0.01f, it would be immovable, so that's what I did. Before that, I set the mass, but not very high. I figured that had to be the problem, so I changed the mass of the ground to 1000. I ran the application and it worked perfectly.
Thank you for taking the time to help me with this Julio! You've been a great help!