In general the manual is the best place to check as diferent board use diferent flashing.
Normal steps.
1. Format a floppy disk as a 98 boot disk.
2. Download the biosfile.bin to the floppy disk.
3. Download the flasher to that disk. the names chage from flasher to flasher.
4. Reboot and make sure FDD is your boot device.
5. get to dos and type
a: <enter>
flasher biosfile.bin ..... wait for it....DO NOT power down for any reason. It will reboot when its done.
You can also flash from windows, but i dont do this. Some Asus boards can flash the bios from in the bios
EZ-flash i think they call it and it works with usb drives.
Precaution to take is to never flash at a time when power outs can happen(thunder storm's and such) as a power out can render the system un-bootable. Also make sure you have the old bios saved to disk of another system as sometimes the new bios may not be what u hoped for.
Hope this helps some