T61 Fan shutdown temp?

I'm

I have replaced my main Thinkpad with a new T61. Very silent. Although I have found some issues or doubts regarding the temperature readings on the TPFancontrol software against another reading software such as HWMonitor.

In NBR forums there's the Undervolting Guide:
http://forum.notebookreview.com/showthread.php?t=235824 suggesting the use of Orthos + HWMonitor + RightMark CPU Clock Utility.

I followed that guide to undervolt my T8100 45nm processor. Then installed TPFanControl v0.50. HWMonitor temperatures from the Cores 0 and 1 are different than the 'CPU' reading on TPFanControl.
TPFancontrol reads the THM0 value as CPU. In my opinion right now in the T61 is useless to control the fan because we're getting a totally different reading.
Here, take a look at this screenshot.


You can clearly see there's discrepancies on the CPU reading.

Yesterday I wiped the HDD that was preinstalled with Vista Home Premium and downgraded to XP Pro. I don't know now why my fan won't stop working once it read the threshold to start spinning.
I remember in Vista the fan would stop but in XP is not.

I've been working with your 0.18 version (quite old) on my T42p for quite sometime, and now I'm unfamiliar with the new values the TPFanControl has:

1 cpu 42°C (0x78)
2 aps 41°C (0x79)
3 crd 34°C (0x7a)
5 no5 32°C (0x7c)
7 bat 30°C (0x7e)
9 bus 38°C (0xc0)
10 pci 40°C (0xc1)
11 pwr 37°C (0xc2)

against
ACPI
THM0 42C
THM1 30C
Intel Mobile Core 2 Duo T8100
core #0 31C
core #1 28C

What's the CPU temp where the fan on the T61 should stop?? I'm using an 4:3 SXGA+ model.