DEBIAN
======
etch

    * Look at /proc/cpuinfo to determine your CPU and the cpufreq module. If it's a Pentium, you can try p4-clockmod, powernow-k7 for AMD, or acpi-cpufreq for both. Well, if none loads, let it go, it won't work unless you get newer hardware or maybe newer kernel.
    * Add this module in /etc/modules to get it loaded at boot time.
    * Run apt-get install cpufrequtils
    * Edit /etc/default/cpufrequtils to enable it at boot time, and specify the governor if you want. I usually use ondemande, which is just fine.
    * Run /etc/init.d/cpufrequtils start
    * Play with cpufreq-info and cpufreq-set as you wish.

lenny

    * Run apt-get install cpufrequtils
    * Edit /etc/default/cpufrequtils to enable it at boot time, and specify the governor if you want. I usually use ondemande, which is just fine.
    * Run /etc/init.d/loadcpufreq start
    * Run /etc/init.d/cpufrequtils start
    * Play with cpufreq-info and cpufreq-set as you wish.