my buddy is running his 2.4 p4 at 300FSBx 12
my other pc is a 3.0p4 running at 235FSB x 15
tiny, as soon as i pulled up the bios for the first time, it gave me two predetermined speeds, the 2500+ i paid for and 3200+
when you boot your computer, hit delete as it is turning on, this will take you to the BIOS, and assuming you have non-OEM (hp, compaq, etc) will give you options for cpu clock, agp/pci frequency/voltage etc.
do NOT fool with it unless you understand exactly what you are doing,
if you fool with it and it wont turn on, move the CMOS jumper from the 1-2 pins, to the 2-3 pins for a few seconds.