Use your browser's "view source" on the page and steal their javascript...
It’s called the Parallax effect. It’s a popular website trend going on now. I just used a theme for one of my client’s that uses this.
You can see the theme I used here: http://demo.drythemes.com/index.php?theme=dry-wp
Basically think of the New York Times building image as the main background. Instead of it scrolling with the content on the page (when you scroll down), it stays still and the content scrolls over it. With a good, detailed, hi-res image this effect can bring some life to an “old” site’s content.