Hi. I've designed a website for a property company. On the pages that offer details about individual properties I have a layout that consists of a large main image and then a series of small thumbnails underneath. What I need to do is set it up so that when you click on one of the thumbnails the image appears in the place of the large main image, NOT open in a new browser window. I've heard this is a Java effect. Can anyone tell me how I can achieve this?
The only thing is, I don't have the option of having images on separate pages or anything like that. I'm using bespoke software through the company I work for and extra pages will cost the client £49 PER PAGE! So I need a way of doing this without requiring an infinite number of separate pages. I can upload any number of images/documents etc, but the number of actual pages is fixed.

Some help would be greatly appreciated!