I usually make layered templates from any sketch that I work from so I can reuse it later. The process goes pretty fast. Just make sure to put each separate part of the template on its own layer. The tutorial section has a tutorial on using layered templates in PSE 3 that might help you develop your own template and possibly help with the PNG files. Did your PNG template set come with instructions? Sometimes the designer includes instructions for using the PSD template and the PNG format for templates.