I am creating a Game Engine, trying to use Havok physics, I am not quit sure about how I should deal with the Physics Engine.

What I know is that I have a world, hkpWorld, and I have RigidBody, what I should do is that I add RigidBodies to hkpWorld for physics stimulation, however, If I have a tank mesh (made in 3Ds Max) and this mesh is using 2 boundary boxes, one on the tank body, another on the tank cannon, should I add each boundary box as RigidBody?

How RigidBody will be stored like? will it store the whole tank mesh or just the boundary boxes?

This has nothing to do with DirectX... moving your thread.

Try posting on the Havok forum. They're usually pretty good about answering questions about use cases and such.

http://software.intel.com/en-us/forums/havok/

A rigid body is "rigid", in that it's one solid block that can't be bent or broken -- once you attach shapes to it, those shapes are always in the same position relative to each other.

If the tank cannon can't rotate, then both "box" shapes can be attached to the same rigid body.
If the tank cannon can rotate, then it should be a separate rigid body (attached to the main rigid body by some kind of joint/constraint).