Trying to reduce bandwidth usage

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Here's a little background before I start.
Delphielite.com is a php based site. The index page is a template and the content is pulled to the page by PHP. Lately, i've been noticing alot of bandwith usage over the course of a month. This month so far we've used 1.5gb. Most of this was because we hadn't optimized the sites graphics but even by doing that i'm only cutting back a small portion. I found that the problem is that the site has to pull down each of those graphics everytime someone clicks on a link.

Now the question:
Is there any way that I can only pull down the new information and leave the rest of the site alone? It would work something like an iframe but instead of using a frame i want to use php. Let me know if I explained it well enough.