Silly n00b question

If by "preview thumbnail photo" you mean the little picture that eBay shows beside each listing when you do a search, you specify that by selecting an image from the dropdown labeled "Gallery Image" on the lister page next to where you select your images and also checking the "Gallery" box in the Marketing Tools section. I hope that helps!

-- Auctiva David

Thanks David! That is, indeed the picture I was referring to.

I'm sure your tips will help bunches with future listings. Of which there should be bunches. Which means this probably isn't the last time you'll hear from me, alas...

Is there any way to add it now that it's already listed on e-bay?

You might be able to change it if you revise your listing through eBay.

Go to "My eBay" and your active listings. In the pull down menu, which probably says "Sell Similar", select "Revise". Scroll down to the section called "Pictures and Details", and use the link on the right to "Edit Pictures and Details". Scroll waaaaaaaay down to almost the bottom of the page, and see if you can't select "Gallery".

Hope that helps!
From your neighbor up north (I'm in Loveland),
Roxi