Baz, I use the 2 most popular free websites in the world, but neither of them has thumbnail expansion. One of them (Wix) has something similiar, by clicking on the image window it enlarges.
I use Wix for my own website
HERE
and Bravenet for the Snake Valley Camps
HERE
They both have hundreds of ready made templates to use. The ones I use may not suit you but have a look through their range
Wix is the best if you want Flash. Not many free sites give flash.
Wix here:
http://www.wix.com/flash_websites/wi...FZQRHAodgXE8eQ
Bravenet uses the fantastic WYSIWYG or text. It's up to you how you build and edit the site.
.Bravenet here:
http://www.bravenet.com/