You can either raise the fsb....say to 133 or you can do the pencil trick and try to raise the multiplier
the pencil trick may be your best bet on the old athlons. They ran a 100mhz fsb and if you use a pencil to connect the L1 bridges on the cpu you can change the multiplire to 10, 10.5, or 11 and get somewhere around 1000Mhz-1100Mhz. If you raise the fsb go slowly up in say 2Mhz increments booting into windows trying to find that sweet spot. If you go to 133 I'd say try lowering the multiplier and running around 1Ghz or a little higher. Good luck to you with you OC
and welcome to the forums