Okay - this is what I've done in my attempt to get this done today. I must be able to move on to the next step.
I've followed these instructions
http://www.geraelindsey.com/zencart-1-3-8-tutorials/how-to-edit-the-zencart-header-image
They seem pretty simple and straight forward.
I went to this file on my site
yoursite/zencart/includes/templates/classic/images
I uploaded the new header named the same. It didn't change, so I changed the name of my file to be more easily recognized and distinguished by me and uploaded it. No change, so I deleted the other one I had upload AND the header_bg that was already there and still no change on the site!
So, I followed the instructions for using the CSS. No problem. I opened and it opened in Dreamweaver. I found the section to change and gave it the name of the file I had just uploaded, even changed the height to 225, pressed the save button in Dreamweaver. Closed it down. Refreshed my website and NOTHING!