Ubuntu – How to debug an overheating problem on a Dell Inspiron 1564

I have a problem with my Laptop (Dell Inspiron 1564 Core i5 4GB Ram VGA ATI Mobility Radeon HD 4300 running Ubuntu 10.10 32bit). It shuts down abruptly without even a lag in the application I am working with before shutdown. I think it's overheating problem. Actually the laptop is hot all the time when I am running Ubuntu. When I switch back to windows, even with intense load it won't shutdown or show any problem as long as I keep proper ventilation (when the air openings are blocked it does the same).

Actually on Ubuntu i don't usually do things that need much CPU power, usually surfing internet, coding web pages and sometimes playing with python and ruby. I am not enabling desktop effects so no GPU load except the normal GNOME gui.

Now as I am writing the Processor load in the panel monitor applet is 0%, Memory 11% by programs, 22% by cache. And i have CPU Frequency monitor for each of the 4 cores set to 1.20 Ghz (the lowest possible value, i am not sure if this applet does really limit CPU usage). Running sensors in terminal gave me

temp1:       +26.8°C  (crit = +100.0°C)                  
temp2:        +0.0°C  (crit = +100.0°C) 

hddtemp /dev/sda at the terminal gave me

/dev/sda: WDC WD3200BEVT-75ZCT2: 46°C

All that fine but the laptop is Really hot i can feel it in the keyboard, mouse pad is painful to touch, and the fan is always spinning. I am also placing 2 small fans running on USB under the laptop right now and the laptop is lifted over the fans so it's well ventilated.

When I am running windows it doesn't get that hot except when there is a really big load on the CPU and this is keeping me away from using Linux for everyday tasks.

Actually I don't care much for speed as I can deal with low speed it's not going to shutdown abruptly.

So please if you can help me and tell me what are the possible causes, where should I start ?