do you want to flash the current bios and upgrade it, or is it fried and you need a completely new chip.
to flash, find your motherboards model number and manufacturere(MSI, Shuttle, Tyan, Abit, Asus...list goes on) www.makersname.com
just take the side of your comptuer off, both are usually written in on the top side of your mother board, there are also free programs out there that find out the info by running them but i always have bad luck. i prefer the open and look method.
they will have a downloads section, you go to that seciton and find the updated bios seciont and they usually have dirrecitons in there, follow them to the T!!!!
purchase a new bios, you need to know the same thing for sure, after that i have no idea, you might be able to get one from the maker also.