Multi Screen with your iBook, iMac or eMac [Upd.]x3

The newsletter "c't" (Germany) has written an AppleScritp that is supposed to activate the dual-display on iBooks, iMacs and eMacs that are equiped of GPU able to support this display mode. It should save you to have to change the open firmware settigns by hand. By zapping the NVRAm you should get back to the default settings.
OS X is compulsory to run this script. if ou have an iBook with 16 Mo of VRAM, activate Quartz Extreme, with PCIextreme, which can also be found on the linked page (those with a Rage 128 will not be abel to activate Quartz Extreme, it is only for the owners of Radeon). Woth noting alos is the script: "iBookkScreenEnhancer + Desktop", for those who would like to use the external display while keeping the iBook closed. We have not yet heard from users testing it, and have not had time to test these scripts.
You can find the scripts HERE.
[Upd.] First feedbacks are extremly negative! One user has lost use of video on his/her laptop. We advise you not to use any of these scripts in the current situation!
[Upd.] The developper seems rather careless, as the script tries also to patch machines that cannot support the changes !
[Upd.] As Raphaël advises, it is highly recommended not to close an iBook while using an external display. The heat cannot dissipate well and could provoke markings on the screen.