In the latest version of Wordpress it gives you the opportunity to view a preview of what your site would look like using a different heme. You basically just click on the theme and it takes over the screen and you have a chance to activate it or close it (and return to the previous screen, which is grayed out in the background). I have seen a similar technique used on a number of websites recently for display images as well.

I'm wondering what technology/code they use to do this?

+2  A: 

It's open source - use the source, Luke.

Look in wp-admin/js/theme-preview.js

Paul Tomblin

Thanks Paul, that has led me to the answer. The effect I'm looking for can be achieved using the ThickBox widget with jQuery. It works great.