XBOX 360: where do i buy this storage device ( picture )?

You can buy an xbox 360 hard drive from anywhere. Wal-Mart, Target, Bestbuy, ebgames, gamestop, amazon, ebay. There are several different sizes 20gb, 60gb, 120gb and 250gb. The link has a list of all of them so you can see how much they cost and decide which one you want that way.