My previous post generated a lot of useful comments. Some of them was about using the synaptics trackpad driver. Unfortunately it only works, as Itai Seggev says, on post July 2005 iBooks and my iBook seems to be from August 2004 (this fact took me a long time to realize).
I found an adbsyn howto wich seems to have an solution. Using a kernel patch and a patch for xserver-xorg-input-synaptics you can get the ADB Trackpad to simulate a synaptics trackpad. So for the first time i a very long time I get to compile a kernel...
After a very long time I get to reboot into my new patched kernel and, lo and behold, synaptics works. In the beginning i didn't seem to work, I had a very low acceleration set but with some fiddling I got it ajusted to something useable. So for enabling synaptics on older ibooks, see: http://www.cs.unibo.it/~bigoi/howto.htm
In the meantime I got glxgears turning smoothly. Now I can start compiz and see a wobly effect when I move windows around, but then compiz freezes the display. Most of the times I seem to be able to terminate the xserver, but i've reboted once.
Steps to get OpenGL working:
Driver "radeon"in the Monitor section of /etc/X11/xorg.conf
apt-get install libgl-mesa-dri