Note: I take no credit for finding this hack. It was originally posted to the website http://macparts.de, where you can find a german version of the instructions. Also, I will borrow directly from the author of the page and state:
Please note that I cannot be held responsible for any damage that you might do to your computer. This (information) is for educational purposes only and you are responsible for everything you do with the given information.
Now, on to the pure, unadulterated goodness that is multiple-monitor spanning, or
More real estate please!!!
The two most recent revisions of Apple?s iBook, the 700 MHz and 800 MHz, contain ATI Radeon graphics cards which can easily support dual monitors. This option is disabled by default in the iBooks for some unknown reason, but it can be enabled fairly easily. But before you decide to do so, you must determine whether your iBook can handle this hack.
Look in the Apple System Profiler under the Devices and Volumes tab. Click the small triangle next to the PCI entry, and be certain that your laptop?s card is a RageM6 and that the amount of video memory is at least 16 MB (the newest iBooks have 32 MB VRAM). If that is the case, then proceed with the hack. If not, then DO NOT TRY THIS!!! There have been reports of older iBooks not just refusing the hack but in fact being rendered unbootable. Losing your iBook is not a prospect any good Mac zealot wishes to face.
Before permanently enabling writing hack to the firmware, you should do a quick test to make sure that the iBook will accept the modification. To do so, reboot and enter the Open Firmware editing console. This is performed by rebooting your iBook and holding down Command, Option, O and F simultaneously as the laptop boots. A white screen will appear with a little command prompt. Enter the following commands exactly as written below:
Note that those are eight zeros, and not capital "o"s. Here, I have used ← to signify the return key, and _ to signify a space. After typing "mac-boot", your iBook will reboot with the monitor spanning option enabled for this boot only. This means that after testing this hack to see whether it works, when you reboot your iBook will revert to its initial configuration without monitor spanning enabled.
To determine whether your hack worked properly, first connect a second monitor to your iBook using the video dongle. Then, open System Preferences, and select Displays. On the Arrangement tab, you will find a checkbox titled Mirror Displays, which is checked by default. Uncheck this, and your second monitor should now be an extension of your desktop. If this does not work and you?re certain that your laptop can handle the hack, then you likely made an error in your firmware codes. Try again.
If this works and you wish to retain this configuration for the future, you will have to proceed to step 3 and write the information to your firmware.
Reboot your computer and enter the Open Firmware editing console by again holding Command, Option, O and F. Type the following:
00000000_"_graphic-options" get-my-property 2drop !←
ctrl-c means hold down control, and touch the 'c' key. It is normal that you not see any response from the console as you type the second and third lines, as you are editing a text file.
Your iBook will now reboot with monitor spanning enabled for the future. Should you ever want to revert to the original configuration, reboot your computer while holding Command, Option, P and R to resent the nvram. Finally, if your computer only has 16 MB of video ram (as is the case with all of the 700 MHz iBooks), you need to edit a file to enable Quartz Extreme on both monitors. By default, it is only enabled when 16 MB of video memory is availalbe per display, and monitor spanning cuts the video ram in two. So, open the file
and find the section titled GLCompositorMinimumVRAM (you will need superuser privileges to do so). Change the value from 16 to 8, and you?re ready to fly!