You need to make sure that when you are zipping up the files, you go inside the folder that your creation is called. Then, select ALL of the folders in there (like entities, lang, ai, ui, locations), right click and "Add to Archive". If you zip them up when they are still in the, for example "Dog" folder, then the game will not recognize it. Also, it will not recognize it if you do not have a .dl, in which case you need to put it in the MAIN ZT2 install point (default is C:/Program Files/Microsoft Games/Zoo Tycoon 2) NOT the downloads area. Hope that helps