Once you install Picturenaut 3 onto your system (download from HDRLabs.com) and added the Banty's Toolkit plugins to the appropriate folder (download the same place), open the program and either open an HDRI or drag & drop the image into the view window.  As illustrated below, navigate to the Filter tab on the toolbar above, open the contextual menu, and select HDR Shop and scroll down to Diffuse Sh SSE.