most likely celsius. I have my sempron to run an alarm at 68*C and force a shut down at 70*C. and for my mobo (assuming you mean the case temp) i have it set to alarm at 50*C and shut down at 52*C.
so far at full load my cpu was only able to pull 53*C
and my case was 42*C. so im quite confidant in my system.
also i might add that upon the cpu fan falling below 3000RPM (normaly 5000) it will force a shut down.
Might i also add that my current temps are.
CPU = 46*C
Case = 25*C