How to assign inertia to a node?

Hi,

    I want to do modal analysis of engine & fixture assembly. I'm gonna consider engine as a rigid point mass, so i will create a node representing engine and i will assign inertia (Mass, Moment of inertia) to that. Subsequently  i will connect the point mass to fixture mounts through rigids. I don'no how to assign inertia values to node. Any help regarding this will be of great help to me...

Thanks!!!!