Maybe UNDERvolting the P4PE-X ?

Hi everyone! I'm just another person seeking for help I live in Thessaloniki that is a perfect city for students as people say.
Anyway,back to the problem.

I have a P4PE-X motherboard that served me ok untill now.I was using a Celeron 2.4 for the past 3 years.
I found a P4 HT 3.2 over eBay and I bought it.The installation was ok,I think.

The problem now is that at room temperature 28Celcius the CPU sensor reads 52-53C at iddle (PC does nothing).
When I try to play a game or an application that takes the CPU usage high then I get 68C after only 2-3minutes.
Finally the PC hangs up obviously because of overheating.

I noticed at Intel's site that my "new" proccessors' specific voltage is 1.25-1.4Volt.
My Asus motherboard over a BIOS setting can give 1.55Volt at the least.
So,I think that this CPU overheat is because of running the CPU at a high voltage(!)

I have the latest BIOS revision (1007) update,thermal paste MX-1 by ArticCooling and a copper Zalman 12cm fan running at ~2300RPM(its maximum).

Is there any way to lower the Vcore of my P4PE-X?
Thanks!