LightBox2 is a fully customizable and ready-to-use extension to take control of your products' images and showing up them in a wonderful and well-managed way.
How to Download LightBox2
http://www.magentocommerce.com/magento-connect/lightbox2.html
https://github.com/lokesh/lightbox2/archive/master.zip
https://github.com/lokesh/lightbox2/
Steps To Add Lightbox To Magento Theme
1. Make a directory called /lightbox under /skin/frontend/default/default/js/ and copy the entire lighbox code under that directory.
2. Once done, your directory will look like /skin/frontend/default/default/js/lightbox (all code under this directory)
3. copy the lightbox.js under /magento/js/lightbox (create a folder under js directory and name it lightbox). If you installation is under root directory then copy it under /root/js/lightbox
4. Now, you should copy the lightbox.css to /skin/frontend/default/default/css directory.
5. Create a folder called lightbox under /skin/frontend/default/default/images. Your directories for images will finally look like /skin/frontend/default/default/images/lightbox. Copy all the images from source lightbox directory here.
6. Changing Lightbox default’s As Per Your Magento Theme
Change Image Directory Location Of The Lightbox
Once you are done with the above pre-requisites change the following code by editing /skin/frontend/default/default/css/lightbox.css
find the following line of code
background: transparent url(../images/blank.gif) no-repeat;
and replace it with
background: transparent url(../images/lightbox/blank.gif) no-repeat;
I hope it would be helpful for you, however I would like you to post any comment if have any issue.