1. Add needed JS and CSS to you templates
There is few ways to do this and one of the simpliest is to use Calguys Lightbox module. Install it as well needed CGextensions module. Add {LightBox action='css'} and {LightBox action='js'} to head of your page templates like in instructions. If you need to configure something open action.js.php file in /modules/Lightbox directory. There is also other ways to do this.
2. Open in CMSms Admin "Extensions" -> "TinyMCE..." and look for "advanced" tab. Add:
Code: Select all
extended_valid_elements : "a[name|href|target|title|onclick|rel]",
3. Add thumbnail image or text normal way to your page. Select that and press "add link" button and browse to make a link to larger image and from "advanced" tab look for "Relationship page to target" and select "lightbox". Save/apply and you should be all set to test it.
Remember that lightbox uses scriptaculous/prototype library and you will most likely run into problems if you are using mootools, jquery or some other library at the same time. For those you need to find other suitable modal window JS.
Hope ithis works for you!