You can use the free MED from the GameStudio download site. It has bones animation. You can save a model with bones animations as a model without bones animation, then MED transforms the bones animations into vertex animations. Just save it as .mdl5.
(Attention! Try this first: save a model with the free MED as .mdl5, then open it in the MED of your current A6 version! I'm not sure whether it is compatible. It should work with A6.6, but it doesn't work with A6.34.1 for instance!)

"Rigging" is to connect the mesh of your model with the bones.
(At the other terms search by google, it should be easy to find some explanations.)