end product will be like this site..
however, a much simpler site than that..
Only one design template ..
A circle ..one size
visitor creates an account.. is shown the circle template in a flash design editor..
they are able to choose background color text color and select an image from a library or upload one.. image scaling needed to fit the circle template.
They save their design, complete the order and print their results on their own printer.
any standard open source cart is ok as a base for ordering .. such as oscommerce