Lesson learnt. I thought my notebooks were clean since I didn't see any dust around the fan openings nor other openings. But then, I tried using the compressed air anyway and blow it at those area. Although I didn't see and debris, somehow my notebooks now run around 55-58C only (compared to 66-68C earlier). The HD that was running around 55C suddenly only hit 46C max.
in my notebook? Can someone give me an idea where to start (BIOS, etc). It's really weird how my pentium M notebooks' fan almost never run although the temperature gets high. It may run for a few seconds and lower the temp by 2C and than quit. The motherboard temp has been going up to 60C-65C often. I read at Intel website that it's still a safe temperature but the laptop case gets too hot for comfort. I really don't mind the fan running a little often.
I'm sure this is not the notebook's defect. It happens to all my small size pentium M notebooks. I wonder if its the tight casing that cause the excessive heat. The larger size notebooks I have never had this problem and always run cool.