1) Whether a chip overclocks or not is a crap shoot. Some do some don't. You can typically get 5-10% but some chips do not overclcok at all.
2) The MB and Bios have to be overclocking friendly to get good results. That means CPU voltage adjust, FSB adjustable in 1% steps, AGP/PCI/PCI-e clock speeds must be independent of the FSB speed, RAM clock speed must be independently adjustable wrt the FSB, a software overclocking utility included and good thermal protection. Note many "name brand" PCs do not allow any overclocking.
You step the FSB up 1% at a time, run a burn in utility (sisoft sandra has one) and run the system for 20 minutes watching the CPU temperature. If it stays stable you increase it another 1% and repeat. You can jump it 2-3% at a time but it adds more risk of crashes and/or data loss.
If the AGP/PCI/PCI-e clocks are not independent of the FSB DO NOT OVERCLOCK. Video cards are much less tolerant of damage than CPUs and RAM.
If your RAM speed is tied to the FSB speed overclocking may not work. If it doesn't you have to relax the ram chip timing settings in bios.
Software overclocking is best if your MB supports it becasue if you mess up you just reboot with minimal risk. If you overclock the Bios then you have to do a CMOS reset which can wipe the Bios on older MB's.