How to prepare bootable USB stick for Lenovo PC BIOS flashing

This post is actually a note to self how I’ve done it…

Steps taken from:

• http://theendoftheuniver.se/ramblings/creating-a-bootable-usb-on-a-mac-for-flashing-the-bios-on-an-hp-n40l-microserver/
• http://derek.chezmarcotte.ca/freedos-1-1-usb-boot-image