HLT (halt) instructions are used by good operating systems to keep processors cool — the halt instruction is sent whenever the processor has nothing to do. However, HLT’s impact can be unpredictable on multi-processor systems, so Be does not enable the feature by default. If you have a dual-CPU setup and want to give it a shot, open ~/config/settings/kernel/drivers/kernel and add the line

hlt

Save and reboot. If your machine remains stable, you’ll notice your CPU temperature dropping (use Sensor2 to monitor CPU temp). Otherwise, remove or comment out the line and get your stability back.
As one user said of this technique:

Thanks, it worked a treat! Temp fell by 12c on both processors within minutes. Well, that’s another Be convert. I’m just off to delete my NT partition 🙂

Note that using the HLT instruction is kinda useless if you use Seti@home or other number crunchers running, because your processor is never idle.