ThermographX has been running fine on my PowerBook G4 from OS 10.2.8 up through OS 10.5.8. However after stepping up to a new 2.53 GHz Mac Mini, OS 10.6.1, ThermographX days are sadly over. Fortunately several alternatives exist for Intel hardware.
ThermographX, RIP!
ThermographX
CPU temperature monitoring utility
Version: 1.4.0