That's true - this is a digital processing matter, but to be helpful to the OP, it would be good to know what program you are using. If you are using Photoshop CS3, by far the best and most convenient way of doing this is with a Black and White Adjustment Layer. Alternatively, if you wish to open your JPEGs in Lightroom or Camera Raw 4.x, you have similar technology at the raw processing stage which is very good. Finally, if you use an Epson printer which has an Advanced Black and White capability in the driver (ABW), it also does a very good job, and you can produce a whole range of tones from it; the B&W is "pure", but the drawback is absence of soft-proofing capability.