The reason the shopping cart images did not display is that I installed WP from the hosts control panel. Yes I know how to do it manually but I THOUGHT I would be saving time. The hosts' installation uses a totally non-standard directory structure and it broke a lot of stuff including this. You would think they would know better.
Lesson learned: Install WP manually with FTP and don't trust the host.
I have the WP Simple PayPal Shopping Cart installed and so far it seems to be working OK, but whatever it's doing to call the images for checkout, delete, etc. it's calling a crazy, totally wrong URL and the images are not showing up. I know for sure the images are installed.