I don't know about CS3 but in cs2- go to Window>animation
This will give you a window with one 'cell', whatever you have on your canvas.
Make all your layers except the bg transparent. This will take them off of the frame.
Use the controls on the animation window to make new frames (you have to start out with one, then you can add a group).
To animate, you must have your parts you want to show on different layers. You can use multiple layers for each frame.
To make a frame, select the frame on the animations window.
Make the layers you want visible.
You can also move things on layers for each frame and it will remember. For instance, you can make a ball 'roll' by dragging that layer through the frame (select 'cell', select your object. Move the object a little. Select a new cell, move it a little more, etc).
In cs2 you can't save the animation as an actual animation (just as a layered file), you have to send it to another program to save as an animation. CS2 comes with imageready, that is good for gifs. Back when I messed with animation I usually used Macromedia to finish them (drawn in PS), I know it's not really around anymore but there should be an equivalent program.
You'll need to check about that with CS3.
This was done in CS2, I think I finished up the animation in Macromedia. I like the hand-drawn look. I did some other ones, too, but they aren't up here.