Here's a really quick breakdown of the workflow:

• Make a <div> container and set the overflow to hidden.
• Inside that container, create one <div> for each item.
• Place the items in a row, using CSS. Some of the items will end up outside, that's a good thing.
• Using JavaScript, change the placement of all the <div> blocks when a button is pushed so that the entire row of items move.

You can use MooTools for replacing the <div> blocks, it's simple to use and you can get some good transitions.