Sometimes the BIOS can overclock the CPU dynamically for you, through an 'AI' mode. If you have this option, it's all you need to use. But in most cases you tweak the CPU speed by adjusting the frontside-bus speed settings. Within the BIOS, raise that value by 5-MHz or 10-MHz increments, save the changes, and then reboot.
If your PC fails to boot completely--that is, into Windows--go back into the BIOS and return the bus speed to the previous setting. If it does boot successfully, restart it and repeat the process, incrementally raising the bus speed again. After you've made a few increases, run Prime95 for about a half-hour to exercise the CPU. If the system remains stable as this prime-number-generating software taxes the processor, continue to raise the frontside-bus speed slowly.
If you notice performance problems and crashes, or if the CPU becomes too hot, back off the speed until you discover a stable setting. Consider upgrading your CPU's heat sink to keep it cool; a heftier heat sink can allow you to raise the bus speed a bit more.
Overclock Your Graphics Board
Difficulty: Easy Time: 60 minutes
ATI and nVidia each offer free tools to overclock some of their higher-end video cards. This tweak doesn't require any BIOS tuning and can boost your system's graphics performance. Gamers will see smoother video as a result of the faster speed. Update your graphics board's drivers before you begin.
In the nVidia Control Panel, click Device settings under Performance. Click GPU, select Custom, and raise the clock speed by moving the slider, testing the results each time for glitches.
For ATI cards, launch the Catalyst Control Panel. Click Auto-Tune in the Overdrive section. This option gradually increases the clock speed and tests each one in sequence. When it detects instability, it backs off, settling on the previous rate.