thats the best way to update a BIOS, under DOS. Get a USB stick, and format it to FAT32 (a type of file system that almost any OS can read) and then make it bootable. also, FORMATTING WILL "ERASE" EVERYTHING ON THE STICK.
Files and instructions here:
Bios-boot-usb-stick - Howto: BIOS-Update per bootable USB-Stick - www.biosflash.com
Go to ASUS and download the BIOS file. In the BIOS file page there should be a file called AWDFLASH, AFUDOS, or something along those lines to update the BIOS. Download that and place both the BIOS file and program onto the UBS stick (dont create any folders or anything, just put both files onto the stick).
Now here is the tricky part. Plug the stick into a USB port and restart the computer. When its restarting, you can do 1 of 3 three things and I will list the easiest first:
1) Tap delete or F2 or whatever it is to get into SETUPS or BIOS. Under BIOS there might be a section where ASUS already has a built in program to help you update it. If there is, follow the instructions.
2) When the computer is booting, you can tap a button to get into booting sequence, order, or whatever they call it. Then choose USB from there. Continue to 4)
3) Tap delete or whatever to get into the BIOS and manual select the booting order and make the USB stick first. Itll probably be under hard drive section if you cant find it. Continue to 4)
4) After booting the UBS stick first, you'll be in a DOS screen. Depending on which program you use, itll be a little different. Ive used AWDFLASH the most, so i just typed it 'run AWDFLASH.EXE' and a GUI popped up and i just followed the instructions. you dont need to save a copy of the BIOS unless you want to.
heres up if you use AFUDOS:
http://www.ecs.com.tw/extra/flashutl/DOS Flash Utility User Guide.pdf
Good luck with flashing. Oh yeah, DOS is better because its least likely you'll crash, hang, software conflict or something in the middle of flashing which will brick the motherboard. Make sure when you're flashing, it wont be interrupted or lose power.