software kill switch

I've encrypted my disk, but I need a way to prevent somebody from stealing the computer while the encryption key is in RAM.

Basically I need to write a program that writes zeroes to the memory and then cuts power to all devices. The problem is, I don't know exactly how to accomplish this.

Advice preferred in C++ or assembly, but anything would be helpful.

>>9
Yes, but it's faster to just turn the power off if you have more than 640K RAM. It comes down to a matter of have many seconds you have from the time the intruder is detected until they get physical access to the computer.