Many motherboards have a setup option in the BIOS where you can set the
front side bus (FSB) speed for the processor. Except for Intel boards of
course ;-)

Try looking up why you can't simply overclock an AthlonXP processor without
unlocking it first.

An AthlonXP with a locked multiplier will only allow you to attempt an
overclock by adjusting the FSB speed, but tweaking with this setting will push
the processor's clock speed to unstable and potentially damaging levels.

In my case, the multiplier in my Athlon XP 2600+ is locked at 12.5 and cannot
be changed unless it is modified. If I attempt to run the FSB at the next
higher setting, which is 200 MHz in my case, it will push the processor up to a
clock speed at approximately 2500 MHz (the rated speed with my version CPU is
rated to run at 2083 MHz), which means the processor will run unstable and will
have a tendency to cook itself even with the best cooling setups short of using
liquid nitrogen. Even a watercooling setup won't protect my Athlon running at
THAT speed for very long!
Of course, this assumes that the BIOS doesn't detect the overheat and shut the
machine down automatically in reaction.

Further assumption is whether or not Windows would even boot up successfully or
stay running for any appreciable amount of time.

You have to modify the processor in order to allow adjustable multiplier
settings so you can better control the kind of speeds that you are trying to
push the processor up to.

Right now, since my multiplier is locked at 12.5, I'm running it at the
recommended settings. - Reinhart