Here is another link showing you how to carry out this process using a gradient map.
I have been looking into this all night and although it is not classified as a tru duotone i think for this topic most people should be able to acheive an end result no matter what Pp programme they have.
Sepia is not the only colour that you can use by the way.
LINK
http://m.youtube.com/index?desktop_u...?v=EtmzZQNgJkQ
Just trying to follow the theme that Chris started the monthly competition with which was a "photographic technique"