Your best bet is probably with software overclocking using something like SoftFSB or CPUFSB. If your BIOS has no overclocking features whatsoever built in (not just disabled ones) it would be a very impressive amount of work to add them, if the hardware would even support them. The closest I've ever seen is Cheepoman on the OCworkench.com forums (ECS section) who modified BIOSes for the K7S5A to include more FSB options. This was accomplished through a lot of work, and because earlier versions of the bios had overclcoking settings. He compared the differences and figured out how to unlock/program in extra FSB settings that were supported by the PLL-IC on te board. Multi support wasn't in the hardware, although a hardware mod was possible to enable selection of new multis through dip switches that could be glued to the board. That bios mod is beyond my abalities, and simple compared to programming in new bios features without intimate knoweledge of the hardware (or of BIOS programming).
If you want to do it, you should probably start with learning x86 assembly programming. There are always overclocking options, but they don't have to involve the BIOS. If software overclcoking doesn't work for you, there is always "turbo-PLL" style mods, that end with replacing the oscillator that generates the refrence frequency with a faster one (after replicating the three or four clock signals that would cause the computer to fail if overclcoked the sligtest bit).
I also suggest you carefully consider the dangers of overclcoking before starting. Don't overclcok anything that you can't afford to lose, especially if you start modding bioses and soldering on your motherboard.
