How to Create a DOS Bootable USB Flash Drive that can ultimately be used to Run DOS from USB, using Rufus.
Authors Website: http://rufus.akeo.ie/
Download Rufus and launch the program
(1) Select your USB Device from the drop down,
(2) Choose the Fat32 filesystem,
(3) Tick the option to Create a DOS bootable disk
Click the Start button to create the DOS Bootable Drive
Restart your PC, setting your BIOS to boot from the USB device, boot and enjoy!