I was using OpenCart and the product page allows you to click on an image to show enlarged versions, plus related images. Fab. Belatedly I realised that the image didn't display in IE 8. I don't know about IE 7.
I was using the JQuery v 1.3.2 which was bundled with OpenCart. The web has a few mentions of this problem, but they recommended tiny changes to the CSS and/or Js. I happily tried those but they didn't fix the problem.I noticed that the demos on the Thickbox web site worked for me, so I used their copy of JQuery which was a recent one. However.... (bah) then the tab display failed. The default tab (for the "Description") remained invisible until clicked. Very boring.
So, on a hunch, I regressed my JQuery library down from 1.3.2 to 1.2.2. (Actually I tried lots of variants). V 1.2.2 was the one which worked for me. I don't like relying on older librarries but at least it gets me out of the fire for now, until I have time to look further. Yeah, when will that be? The downside is that a couple of OpenCart buttons don't work with older JQuery: specifically the little red cross which removes an item from the shopping cart.
Fortunately, the next time I started an OpenCart project, the new source code was v1.5 and the author has swapped from ThickBox to use the "fancybox" package to show packages. This works faultlessly for me, on all browsers.