You can do it by going into the Hue/Sat settings and clicking on the Colorize box. Then Just adjust the Hue and Saturation sliders untill you see something you like.
You could just convert it to black and white using whichever mehod you prefer to do black and white with and then lay a sepia colored layer over it in color mode with varying opacities, but the duotone method gives the most convincing results. Especially if done with tritones.
