The first difference is that on my iBook I cannot remove the optical drive beforehand. The drive is the biggest problem when unclamping the bottom shell. Essentially you have to do the unclamping in the other direction then on the rest of the shell (IIRC for the most part, the withe outer shell has to be pulled outside, and the inner shell has to be pushed inside for unclamping; but in the area of the optical drive it's the other way round, and needs more force). Despite applying considerable force, the material did not break; it is actually quite flexible on this model.
Another difference was that the keyboard was locked on my ibook; to unlock, use a small screwdriver on the transparent screwhead that indicates NumLock (between F5 and F6).
A big issue was that the differences in the pictures confused me about the structure and what to do. But essentially the structure and the disassembly process seems to be similar: There is an outer shell, the inner shell (where the mouse pad is), and sandwitched between them is a metal frame with most of the components (mainboard, hard disk, optical drive). Between the shell parts and the central frame there is the shielding.
To get to the hard disk, you have to unclamp the outer (white) shell, remove the shielding on that side, unclamp the inner shell, and partially remove the shielding on that side. In any case, you want to take the first steps (removing the keyboard etc.) as described by Uli.
Unclamping the inner shell was not trivial, because the speakers and the power connector resisted, but with a little technique and violence we finally got it to work.
Some connectors spontaneously disconnected themselves: In our case the hard disk and the mouse pad connectors; be sure to reconnect them on reassembly.
Below you find the pictures that we took in the process. The most interesting ones are 839 and 840, which show the iBook as disassembled as we got: The display unit of the ibook is lying on the table (display covered by a piece of paper); on top of that lies the inner shell (with mouse pad, keyboard hole, and speakers). At a right angle to that you see the metal frame; the shielding has been bent away where the hard disk is, and you see the hard disk sticking out.