Ok for starters head meshes and anything dealing with the head have to be all one piece one can not simply slap some ears on a head export it and comformulate it. their are two ways around this 1) have the game auto add them to the players intentory like the moonshadow race does with elven ears, or 2) actually go in and sculpt the ears on the head in blender (or your favorite 3d moddling program) as far as the body it concerned: the tail can be anchored to the upperbody if, if you dont know in new vegas the upper body.nif is the body with out the hands and head and most oblivion lower body nifs can be placed on the upper body with minor alterations. the tail cannot have any tail bones (ie bip tail01, bip tail02, etc) as the nv skeleton has no way of dealing with these bones in game. but it all boils down to using Nifskope and blender (or 3dsmax,etc) the fact is you'll do very little in geck besides linking the meshes to a new race in game, Example: