It sounds to me like your CPU may be 80C, sometimes detectors can be confused, you really must watch all sensors and don't let any of them get above 60C (except for GPU).
To overclock your CPU or memory it is essential that you have modified the VCore at least a little, this adds stability and increases temperature.
My Barton XP2500+ (1.83GHz, 333FSB) is overclocked to 2.2GHz with a VCore of 1.70V - temperature is about 50C under load. I had the option to change my multiplier though.
[size=0.5]Full Aluminium ThermalTake Case
AMD Athlon XP 3200+ *400 FSB* Barton (2.2GHz)
ThermalTake Volcano 11+ Xaser Edition Air Cooling
1024MB Corsair TwinX XMS 3200 (Dual Channel 2x512) 2-3-2-6
256Mb XFX 7800 GS EXTREME
2x WD Raptors (10krpm 8MB Cache) 36.7GB using RAID -0
Video Logic SonicXplosion 5.1 Soundcard[/size]