BTW, you can't add any form of color to a truly B&W image, either "grayscale" or "bitmap" in Photoshop-speak. You can only do it with a color image. The trick is that after converting the image to B&W by what ever method you like the image must be converted back into an RGB, or other colorspace, image. If you leave the "Image/Mode" in "grayscale" or "bitmap" you can't apply colors.
Personally, when converting a color image to B&W, I usually use a "Color Mixer" Adjustment Layer to do the conversion to monotone. The image data remains a 3 channel "color" image. You can then colorize the image using a variety of methods. One is to add a "Hue/Saturation" Adjustment Layer and check the "colorize" option. I skipped PS/CS3 so I don't know if it has the same Adjustment Layer presest as CS4. In CS4, there is a preset for the Hue/Saturation Adjustment Layer to produce a decent sepia effect.