It depends on if the model is comprised of a single mesh or multiple parts. If it is multiple parts then each child object is a separate entity and you can just use EntityAlpha. If the model is a single mesh you will need to use the alpha channel of a TGA texture. Note however that setting alpha on will remove z-buffering for that object so, to avoid serious draw order problems, you will probably want to go with the first method and actually model the semi-transparent parts as separate objects from the rest of the mesh. In other words the glass over the jet is a separate child object attached to the jet.