If its done in dos or a built in program on the bios chip the chances are vary rare to fail(willing to bet its less then 1%). There are just too many variables when flashing from windows(thats why most people around here will not recommend it).
back on topic
Do as said above. if that fails try this
Power on the computer and insert the driver CD that came with the board(just power it long enough to close the tray). power the computer off(maybe 10 sec). Power it back on and cross your fingers, with any luck if there is enough bios left it will look on the cd and self flash it self to the bios on the CD. You can also just burn the bios to a CD or us a flash drive or floppy drive.
Its a long shot, but its worth a try.
As said above you can get a new bios chip sent out. sometimes asus does it for free since its there software that messed up. Give them a call and ask about a replacement chip.