Download this FreeDOS bootable floppy disk image named FDOEM.144.gz.  Unzip it, which will give you a file called FDOEM.144.  Mount FDOEM.144 on a temporary mount point:

mkdir ~/tmp_mount_point
sudo mount -o loop FDOEM.144 ~/tmp_mount_point

Download your BIOS update from your motherboard manufacturer’s website, which should consist of a FOO.BIN file and a FLASH.EXE file (of course the actual filenames will differ).  Copy those 2 files into the ~/tmp_mount_point/ directory, then unmount it:

umount ~/tmp_mount_point

Now the FDOEM.144 file contains your BIOS update files, so you just need to write it to a bootable disk/disc.  To write it to a floppy disk, assuming that /dev/fd0 is your floppy:

dd if=FDOEM.144 of=/dev/fd0

Or to write it to a CD, you first need to create an ISO image file from it:

mkisofs -o biosupdate.iso -b FDOEM.144 FDOEM.144

Now just write the biosupdate.iso file to a CD.  In Ubuntu (Gnome), right-click it and choose "Write to Disc..."; or you can use any CD-writer app (K3B, Brasero, etc) to do it.