The Lex 860A EPIA 5000 board uses the 533MHz C3 CPU. By loading the longhaul module - you can throttle the CPU. Note that it became stable with kernel 2.6.11.11 only on my system.
So - all you need to do is enable the longhaul by loading the longhaul module:
modprobe longhaul
Check using the dmesg command to see if it loaded correctly.
If this works - make sure the longhaul module gets loaded at every boot. For this - just add "longhaul" and "cpufreq_powersave" into the /etc/modules file.
Using the longhaul stuff - make sure you use under a 2.6.12.4 kernel-module (as configured in config-2.6.12.4) with the userspace-governor eabled by default - then change to:

# cd /sys/devices/system/cpu/cpu0/cpufreq
cpufreq # ls
affected_cpus
scaling_available_frequencies
scaling_governor
cpuinfo_cur_freq
scaling_available_governors
scaling_max_freq
cpuinfo_max_freq
scaling_cur_freq
scaling_min_freq
cpuinfo_min_freq
scaling_driver
scaling_setspeed
cpufreq # modprobe cpufreq_powersave
cpufreq # cat scaling_available_governors
powersave userspace
echo powersave > scaling_governor
cpufreq # cat scaling_cur_freq
399000

That's it ...