Unless, your computer, was made by a proprietary manufacturer(i.e. Dell, Gateway, etc.
your motherboard, should have a both, an adjustable FSB(front side bus)
which will be in the BIOS. My 2600+ had 12.5x multiplier, now with it at 14X.
Mu 2600+ reads as a 2800+ in the BIOS, & windows, this was before adjusting the FSB.
After adjusting the FSB to from 333mhz to 347Mhz(stepping up one or two numbers per boot, untill it shut off, then I upped to core voltage to 1.75volts(also in the BIOS), at 347 it runs stable an cool enough(still at 38C under full load)
Original CPU core clock of my 2600+ was 2.083Ghz
Overclocked CPU core 2.75Ghz
this was performed with air cooling, I have 3 120mm fans on the top, one 120mm on the side, where the Video card,Nvidia 5700fx sits in the AGP slot(also Oced using coolbits from overclockers.au)

Check with your motherboard manufacturer, for a manual, if you do not have one. in it, you will find where the Multiplier switch, is located on the motherboard, and what settings the pins must ber for each multi setting(i.e. 12.5, 13, 13.5, 14, 14.5) start with 13 reboot, run a benchmark using 3dmarks or similar test, then see what your core temp is.(mnine was at 28C before & now is at 38C only ten degrees C rise for 700Mhz's!!!

good luck, email me, if you want more help,

regards,

PCfixinman