Okay you have some images on a site that you want to show off. You make a thumb nail and a large image and want the thing to pop-up with a cool gray background that covers the web page.

One quick and easy way is with a free (or commercial license) javascricpt call Shadowbox.

I used it last night and it worked like a champ, without any major coding.

the script can be found here

Shadowbox.js Shadowbox.js

Good luck