This sample max file has custom scripted controllers on several objects. The net result is that when you go into walkthrough mode in the camera view, you follow the terain and do not go through walls.

Notes:
This script uses concepts discussed in the scripted controller tutorial.
Press the up arrow to enter walkthrough mode. Notice how you follow the terrain and are blocked by walls.
Replace the plane01 object with your own low poly object to test out your own collison mesh.