diagonising a overheating problem

[Aryeh Friedman]

I have a HP Pavilion g7-1365dx laptop that is constantly freezing up
(doesn't respond to any key/mouse actions except the power switch) at
random times the most reasonable explination I can think of is
overheating and thus I have gotten one of those laptop mats that has a
fan in it but to no avail (makes it less likely but now that stuff is
heating up in late spring [I have no AC]) it is happening again... I
use the machine for totally routine desktop stuff (surfing the web,
watching flash movies and some lite java development).... my guess is
that for some reason the FreeBSD CPU/bus speed controls and such are
not working based on the following item I found in my dmesg's:

acpi_tz0: _CRT value is absurd, ignored (-273.2C)

I have no other clues so far