You can convert your colour photos into Black & White, the setting on your camera that say black & white are not true black & white, they are more greyscale. Depending on which editing software you use, you can get some good plug in software that will do the work for you.
I use NiK Software Silver Efex Pro that will convert my colour images to Black & White
i have the d3000 and there is asetting in set up mode to turn the pictures b&W before you shoot go in to shoot mode then to set picture control go down the menu to select monochrome press ok to select, job done.
I think the best way to do is in post like John said. I tried a couple of times in camera but always prefered having the colour version to play with in post.
I have a d300 and often use the picture controls to for general available light of my kids in the house and it works quite well to give a light sepia look. I always shoot raw and jpeg so I always have the colour version available. see pic below more or less straight from the camera
Picture Control
contrast +1
filter effect orange
toning sepia 2