Any questions about making mods to Nexus can be placed here. Nexus was designed with modding in mind, and Mithis/HDI included mod tools on the game CD's. Other modders have developed popular mods, though total conversions were not really possible. Ship modeling is all done using LightWave, but you will find a plugin for exporting Nexus models to Milkshape, for use in modding (I'm not sure if it works both ways, tho) in the Modding Tools section of Nexus downloads.
Tools are also availble for creating & managing campaigns & missions, as well as adding custom ships & bases, which are also availble to download. 
