Booting from 'Live' USB with a Mac Book

I have both "live" DVD and USB, supplied by a well known US supplier.
When I try to boot from them I get the caption 'the disc cannot be read.'
I think I realise that I am missing something and/or doing (or failing to do) something really fundamentally naive or stupid.
There must be many using an OpenSuSE live USB on a mac - can anyone help, please?

Regards, lim