Go into bios, change FSB, around 5-10Mhz at a time... and slowly overclock it until you get your maxFSB or speed. If it starts crashing too much raise your voltage ALITTLE. If you jump too much say goodbye to yuor CPU. I dont not know much... but if your computer doesnt let you overclock... theres things like SoftFSB that changes your FSB manually without restarting... when yuo overclock and raise voltages a good heatsink and fan, and good thermal paste will help. overclocking also puts strain on the power supply, so get a trusted one that wont die out. Overclocking also depends on your hardware, if you have a stick of pc2100 RAM and pc2700 ram, the pc2700 ram is going to run at the pc2100 ram's speed, so it will reduce your overclockng abilities.
Also: overclocking your CPU or graphics card?