Made some progress today. Setting up Bullet is taking me longer than expected, but at least I'm making some headway. 3dsmax's pro-boolean tool didn't like the tube in the test level, so I had to re-make that part in order to make a few changes to the tube. The results turned out better than I expected. The overall progress of MarbleRun, however, is slower than I expected and I'm worried if I'll be able to meet all the requirements on time... Also had to battle 3dsmax for a while, took me half an hour to figure out that pressing the space bar during "walk-through" mode locks the pitch of the camera! Grawr!