3D Model problems

Hello, I'm a programmer and I've been given some 3d models made in 3ds max. I've imported the character model made for the bootcamp demo for Unity3D, which works fine but when put in the model (of a library in my case) or even on a simple terrain, he simply falls through. Does anybody know how to solve this problem?

I even tried to import the Library model INSIDE the actual bootcamp scene and the character would walk on the terrain but it would also walk through the walls of my model

Any idea???

Add a collider to your mesh.

Components->Physics->whatever collider(s) seem appropriate.