OK, I got you now. You are trying to submit a tour to the showcase page. As I understand it that is just for displaying your tour on the Easypano showcase page of their website as VT of the month. I don't think you should have to put anything in the upload box just hit submit after you have filled out the other information. As for the thumbnail, you will have to host it somewhere such as "photobucket" for free and provide the link/address to it in that box. But if you don't want to showcase your tour then you don't have to do anything.
Hope this is what you were looking for.

Jerry