Hi AFT,
When you are looking at the Auctiva listing creation page, the image that appears in the top section comes from the Select an Image slot labeled "eBay Header" image. Therefore, if you do not want an image to show up in that section, you would simply want to leave that Select an Image box labeled "eBay Header Image" blank.
The Slide Show that I was referring to is the option you selected from the "Image Grouping" drop down menu after you selected the templates for your listings, which makes it so all the images in the description are displayed in one spot within the template and are cycled through in slide show format.
The issue that causes the page to shift as the images in the slide show change is a conflict between that Slide Show image grouping and the fact that many of the images in your listings have very different proportions.
If you open up one of your saved listings within Auctiva and click the "Modify Layout" link next to where you selected your template from, you will see an "Image Grouping" drop down menu in the Customize Layout section on the left hand side of the page.
If you choose a couple of the other options from that menu and watch how the preview changes, I think you will see what I mean.
-Mike