I am not familiar with MAX8 and its plugins, but I suppose the easiest way is through 3DS (if the model has no bones) or FBX (if it has bones).

Upgrade to version 6.60, and then download the free MED version from the lite-C page. Import the 3DS or FBX file in this MED, and save it as MDL. The 6.60 engine can load models that are saved with the free MED.