Non ACPI just gives you two speeds to work with, full 1.8 and slow 1.2.

# echo "1200000:1800000:powersave" > /proc/cpufreq
# echo "1200000:1800000:performance" > /proc/cpufreq

You can actually tweak the cpu through the acpi interface too:

# echo "N" > /proc/acpi/processor/CPU/throttling #where 0 <= N <= 7.