This is a photo from my vacation this summer, some old fisherman's cabins by the sea. I wanted to make an old-looking sepia photo of it and found a very interesting tutorial in a Swedish magazine that I partly used, the result is below. I'm not especially good at making tutorials but I will have a try here to describe how I made this.
There are of course many ways to do this in Photoshop so this is just one way, where you concentrate on the dark areas in the photo.
At first I made the photo black & white, in my case I used the green filter preset in Photoshop CS3. (You can click on the screenshots to have a better look at them.)
Then I clicked on the channels folder in the layers palette, as you can see on the screenshot below . Press Ctrl and click with the mouse on the RGB thumbnail at the same time, (by the red arrow at the screenshot below) There will now be marching ants around all the light areas of the photo.
But it's the dark areas we want to work with, so go to select in the menu and choose inverse (or Shift+Ctrl+I). Now the dark areas are selected.
You can now choose a color of your liking, I chose a brown tone as you can see.
I choose multiply here and kept the opacity 100%, but you can decrease it if you want.