You can visit below link to know how to update BIOS using ISO file.
However model which you are refering D845WN dosen't have the ISO BIOS file to support the same.
I understand that the available latest bios file for your board gives you two installation options only. One option is to use a floppy and the other is through windows. There is no iso file available. Its been a long time since I have done this so I'm not sure but you can try making a dos bootable CD-RW (I'm assuming based on your info that you are able to boot into a cd). Copy the floppy based bios file into it. Boot your computer with the bootable cd. At the prompt, run the bios file.