Pete,
It took me a lot of time and trial and error to figure out how to make the header (banner) appear the way I wanted it to. Anyway, you will need to use the HTML Editor and an FTP program to download, modify, and upload a couple of php pages and the default css file. This has to be done
AFTER you have published your store to your hosting server.
Let's start here....
First, you should learn how size your graphics/photos using pixels instead of inches. You said your banner image is 12" wide. This is too wide. For the shopping cart banner, the image cannot be more than 960 pixels (10") wide.
And, basically speaking, the height is rarely a problem so you don't have to worry about that.
Next....
You can check out my shop (which I'm still adding products to) and hope to open later this month.
http://bottomdollarcomputing.com/
I have also added a couple more pages and modified the footer to my satisfaction. While your at it, you can email me using this address:
owner@bottomdollarcomputing.com
I am willing to help you with the various steps needed to make your store look the way you want it.
Darlene