Debian Sarge on IBM X40 howto - Part 5: CPU frequency scaling

This was quite easy:

apt-get install cpufreqd
apt-get install gnome-cpufreq-applet

Finally add the applet to the GNOME panel.

Make sure that the acpi module is loaded in order to get cpufreqd to run, because without cpufreqd no frequency scaling will happen.

Now when ever you pull the power for your laptop the frequency will be scaled down to 66% until the system requires the recources. This can be cunfigured in /etv/cpufreqd.conf.