maka_why,
Funny enough, I was just searching for this same thing 2 days ago. I also want to update my PC BIOS, though I'm yet to do that.
Please note that you cannot update your BIOS with a flash drive (unless you have the software inside your flash drive), and you cannot flashdrive your PC BIOS.

You seem to be confused with the terms being used here. I'll explain.
Actually, there are two types of motherboard ROM chips. The Mask-ROM and the Flash-ROM. The Mask-ROM cannot be upgraded with software, but the Flash-ROM can. Therefore, you can only update your motherboard BIOS by downloading and installing programs, if it has a Flash-ROM chip (most modern motherboards do, anyway).
I guess what you really want to know is how you can upgrade your BIOS by software. Well, first things first, you should know your motherboard manufacturer, motherboard model, and your BIOS manufacturer. Then all other things shall be made available to you. If you do not want to go through the whole process of checking your BIOS manufaturer, the date and serial during POST (i.e. while your PC is just booting); as well as the stress of deciphering the codes of the serials, then you should download either Sandra, EVEREST, or Hwinfo32. I recommend EVEREST because it also gives you a direct link to download your motherboard BIOS, unlike the others. Download EVEREST here:
http://www.lavalys.com/products/download.php?pid=3&lang=enCheck this page to see how EVEREST works:
http://www.hardwaresecrets.com/article/236/3 See this site for more info:
http://www.hardwaresecrets.com/article/33 (Go through all the 7 pages).
I hope this helps.