There is no such thing as a BM6 running a P2 400.
The term you are referring to is "Overclocking", which is running a cpu above it's factory default speed.
Here is the issue:
The BM6 is a socket 370 board designed for PPGA processors, such as Celerons and FC-PGA PIII's.
A PII was only made in Slot1.
They will not physically fit together.