Dynamically loading continuous scrolling background?

Hi. I was seen this effect on a few different sites, like the back ground on http://www.gap1969.com. It’s like a continuous scrolling thumbnail list but in the x and y direction where the thumbs out side of the screen area aren’t loaded until they are scrolled into the screen.

Has anyone seen any tutorials on the best way to build something like this? possibly an element matrix is being built and if the items are in the screen area they are then loaded?