I export JPEG copies of all the images I want included in the book. Then I use the MyPublisher software to design the book using those exported JPEG's.
Do you mean you just use JPEGs of your images, or do you create JPEGs of the pages in the book module after you create it?
Most of the time I simply load the JPEG images into the MyPublisher software, and drag them onto the page. Occasionally I will create my own page when I want to do something more creative than I can figure out how to do in their software.