Just launch syslinux.exe with '-f e:' as argument (replace 'e' by the drive letter of the USB flash drive). Just launch NTRawrite.exe, enter 'boot.img' and the drive letter of the USB flash drive. It is located in the 'win32' folder of the ZIP archive you downloaded. Everything you need is already installed on your Mac. Don’t get tricked into buying special applications for this. There’s a lot of information on the Internet on how to create bootable media on OS X, and a lot of it doesn’t work.
I wanted to install Debian on my brand new mini-ITX server (with no CD/DVD drive, only several USB ports and an SSD drive), but I only had a Windows machine available. How to create a bootable USB drive from an ISO image on Mac OS X 09-11-2017. This is something that should be obvious, but I managed to lose several days on this problem.
