admin, catalog, categories/products and find what you want to dupe. select the copy icon (blue circle with the 'c' on it) selct the category you want it in (should be the same one as the one your copying by default) and change the copy method to duplicate product. it will make an exact copy that is disabled so you can make whatever changes you need, click the red box under status when your done making changes. repeat ad nauseum.