Download-Manager Lightbox Demo: See Here
First Step: Download the WP jQuery Lightbox Plugin: Download 
Step Two: Download WPDM ColorBox (For additional previews) Download

Hint: WPDM Colorbox adds the additional previews Lightbox effect

How To:
Open: page-template-1col-ex.php
Go to line: 5
replace:

with:

Save; page-template-1col-ex.php
finished

Adjust:

Button Name

Template Code – Default with Lightbox: page-template-1col-ex.php

Template Code (modified) Zorrox.com with Lightbox, jump to description & You are currently here: page-template-1col-ex.php