PCI to FSB ratio/divider Help

I can OC my Athlon 2600+ to use a 170 and above FSB. However, I cannot reset the PCI bus ratio in my BIOS to the 1/5 divider. Therefore, when I get above 170 FSB my PCI and AGP buses are overclocked to a level where I risk data loss. Does anyone have any ideas? Is there some software out there that will let me access and control this ratio even if the BIOS doesn't offer that option?

No software exists on such mobos to allow the 1/5 divider to be manually operated - either the mobo supports the 1/5 divider and it automaticaly kicks in around 166 or it doesnt have it and stays at 1/4.