Overclocking can be done by increasing the multiplier of the processor. It can be done by altering the resistor settings at the AMD K7 processor printed circuit board.
www.tomshardware.com had article on the modding some 4 years ago.
PS. I have one 6167/700MHz PC still running as server. I used to overclock it 1000MHz, but now I run it nominal 700Mhz for reduced cooling and noise level