Athlon XP 2500, cooling

I have an Asus notebook (L3350M / model L300D_L) equipped with
Athlon XP-M 2500+ (system clock 133.90 x 14.0), SiS740 chipset,
512 MB RAM, Windows XP SP1.
The problem is, it shuts down by itself quite often when cpu
temperature rises.
Windows' built-in HLT cooling does not work for Athlon, so I
downloaded several "cooling software". CPUIdle and another one
who have specific AMD cooling options work fine (temperature
drops by ~ 10-20°C), but the systems becomes very unstable,
Windows does not shut down properly and hard disk data gets
corrupted.
I have tried VCool but it doesn't support my motherboard.
Actually I'm using Speedfan, but it's useless for cooling and doesn't
let me change fan settings and voltages.
I really hope somebody here can help me...
Thanks,

Mike