i think you need version 1.7 in order to work with freelancer, not the latest ms version. - you can download the 1.7 version still i think - and use your serial key to activate it. with 1.7, your plug-ins should work just fine.
i can mail you the plugin for the cmp importer etc. -but i can also just send you all the models ( vanilla ) as ms3d versions ( textured ). - and you need version 1.7.0
you can most certainly Email the vendor of milkshape to send you the 1.7.0 version - when you have a legal code, it should be within the customer service. - other than that, you won t get a legal copy of 1.7.0 anymore, not the legal way that is.