Use
RMClock or
NHC. RMClock has more features but NHC is easier to set up.
Set up a battery saving profile, with a 1.6 Pentium M I think the lowest speedstep is 800MHz.
Undervolt the chip with either of these two utils. Undervolting will also improve battery life.
What laptop is it? If it's a Dell you can use
i8kfangui to control the fan manually.
If you want to go further, you could open up the laptop and clean the thermal paste/pad off the CPU and replace with artic silver.
Read and search through Notebookforums.com for your laptop make/model. You may find other solutions.