You gotta love this - straight from the horse's mouth
When you open an animated GIF file in Adobe Photoshop CS3, the file opens with a single layer that displays the first frame of the GIF file, and the Animation palette timeline is empty. If you save the GIF file from Photoshop CS3, the animation frames are lost.
Previous versions of Photoshop included ImageReady, which opened animated GIF files with a layer for each frame of the animation.
Open the animated GIF file in Adobe Fireworks. Fireworks provides editable layers and timelines for animated GIF files.
Adobe ImageReady is no longer being developed. Most of the features from ImageReady have been incorporated in Photoshop CS3. Those that are not included in Photoshop are available in Fireworks.