You have to check out this online tool called The Rasterbator. It’s a script that takes images of any size and turns them into user configurable HUGE multi-sheet works of printable art. The script samples the color from the image and creates resizable shapes that recreate the image.
I made a 90 sheet color poster for my office from this photograph I shot at the fashion show at MAGIC in Las Vegas last year.
(By the way, this photo and many more to come (via Flickr) are from my cool new Nokia 7610 cameraphone.)