After buying the BenQ FW202P flat panel I replaced my old PS/2 keyboard and mouse with USB peripherals, hoping that they'd let me use my iBook in clamshell mode. Of course, I had to apply the Screen Spanning Doctor hack, which allows me to use a desktop that spans over the external flat panel (not in cloning mode). Note that extending the desktop works perfectly at a resolution of 1680x1050, albeit some effects are a bit slow (e.g. ExposÃ©).
Unfortunately, the "unofficial" clamshell mode enabled by SSD does not work properly with this specific iBook G4 model. No matter what I try, the external monitor always gets an incorrect, non-native resolution that is either cropped or expanded in ugly ways. But, as I had already bought the other peripherals (and I do not regret it, because they are much better than the previous ones), I did the following: I connected the external monitor, mouse and keyboard and powered up the iBook regularly. When it got to the login screen, I turned the internal screen's brightness to its minimum so that it didn't consume more power than really needed.
As regards the desktop setup, I stuck the internal monitor to the right of the external one and vertically centered it; this way I'd use the hot corner functionalities in the latter. I also moved the menu bar to the external one, making it the primary monitor. This setup works fairly well and "simulates" a real clamshell mode.
However, I'm not using this setup any more because it's not very comfortable. First of all, it's quite annoying to have to connect/disconnect everything over and over again (which is a mess on the table) and the image in the flatpanell appears somewhat blurry due to the regular D-Sub connection (it worked fine with a CRT monitor). I guess things could be much better if I had a KVM... And secondly, every time you switch between the external and internal monitor, you "lose" your settings. For example, your preferred applications do not appear where you left them, your terminal settings (font size, etc.) are not appropriate both monitors, and a bunch of other little details that make this setup a bit uncomfortable.