Content calling in a Div

i am working on a php website and want to create a dynamic product page similar as the following link:
http://www.interioricons.com/product.php?sid=7

The moving slides are being created by jquery cycle plugin.

when a product is clicked , it displays the product details page (proddetail.php) without refreshing the page in the bottom div. the page url remains the same for all the products in the category.

when i copy the product link and paste in browser (http://www.interioricons.com/proddetail.php?prod=CH7), it also displays the same content (proddetail.php) with header and footer content.

can anybody explain me how the page contents (proddetail.php) are called on 2 different pages - Clicking on any product http://www.interioricons.com/product.php?sid=7) and (individual product link - http://www.interioricons.com/proddetail.php?prod=CH7)

i.e the same page (proddetail.php) is displayed in a div on one page(product.php) with product details div and on the page(proddetail.php) it displays as an individual page with header and footer content + product details div.

thanks...