use an executable to make a just DOS boot disk from the internet somewhere...
i know they are out there, google win98 boot disk
that may work, though if the HD is formatted as ntfs it might not.
you can try un-attaching the hard drive before booting.
i will ask, is there a problem with your MB that you need to upgrade the BIOS? if not, follow the rule "ain't broke dont fix it" with the CMOS.
the "newest and bestest" isn't always good, and if something does go wrong, you just lost the MB.
unless you need to flash the BIOS i would not recommend it. even then i'd look for other solutions