Yup ... it's pretty doable.. Here's the information someone would need to do it..
The IO LED ports
IO port 0x404c bits 0 and 1
The Thermal monitor ports(registers anyway)
SouthBridge (Bus 0 Device 7)
Offsets 0x1f 0x20 and 0x21 are the 3 thermal readouts
Basically have your running program read the input every few seconds and depending on the result switch the appropriate led.
.. you'll want to set it up with a hysteresis(sp?) curve so that it doesn't switch off just to switch back on again 1.5s later..