The new Beta of Adobe Photoshop CS3 includes a new feature to export big images for websites in the zoomify format.
This image is effectively a flash file that only loads the part of the image you’re interested in, so the viewers don’t need to wait for the whole image to download fully before they can look at details. The effect is similar to Google maps. An example of the result is shown above with an optional navigator window in the top left corner.