try this utilty to read temp settings and to control fan speeds

http://www.diefer.de/i8kfan/index.html

This sounds very similar to the problem I'm having with mine. Except the temperature is more like 10-15 degrees celcius. The frustrating thing is that this is within the operating temperature of an Inspiron 6400.

I haven't tried that software as I heard it could void the warranty, but it doesn't appear that Dell has a solution at this stage.
Perhaps a future BIOS update will solve the problem, but until then maybe call their customer support line. It hasn't helped me yet, maybe you'll have some luck.

Today i turned on my laptop and the fan started to spin at high speed, so i tried to monitor my system.

Cpu speed was reported at 800 MHz by BIOS.
CPU temp started at 0°C, while other components (gpu, memory, chipset) were around 16°C.
With cpu fan spinning that fast, cpu temp never got higher than 7°C.
I tried turning cpu fan off manually (by software), until 17°C, but when i stop manually controlling fan speed, it's set to high speed again, lowering cpu temp to 7°C aprox.

Cpu speed never changed, and other components temps didn't change more than 1°C.

As i mention in a previous post, all this gets fixed by rebooting, but it's annoying and i think this should be fixed.

Yeah, it sure is an annoyance...

I haven't had any luck luck yet either. After hours on the phone to them Dell are now sending me a replacement. Hopefully this will fix things, I'm wondering if a BIOS update will be the solution rather than this continuous replacement of parts / computer?
I BIOS update is probably due soon considering when the last one came out...

if you find the solution, please let me know ;)

Update, but no solution:
I recieved the replacement two days ago, started it up this morning when it was cold. Same problem.
Because it was installing McAfee updates it took 27 minutes to start up. I kid you not, 27 minutes.

I'm asking for a refund, I don't have this sort of free time to wait for a computer to start up just so I can check emails in the morning...

Update, and something of a solution:

Dell have approved a refund for the computer. While I'm disappointed that the computer never really worked as it should, I have a lot more respect for them now that they were good enough to put the customer first.

The Dell rep. I spoke to before getting a refund said that they were working on a BIOS update to fix the issue which is due out this month, this might be of constellation to those who have endured this issue...