Costume assets are stored here - APB\APBGame\Content\Packages\APB_CharacterTool
Very interesting how they do their NPC's, too - they use normal maps for different parts of the face (chin, brow, cheeks, eyes - F_Body_Head.upk for the female textures) which combine to create on top of a standard generic mesh to create a somewhat unique face. Well worth a look if this kinda stuff interests you.
Also, if using the build of APB provided here by Tosyk, make sure you move the audio folder *completely* out of the APB folder, otherwise umodel will politely decline your request
