Tutorial: B&W Conversion in CS3
New in Photoshop CS3 is an adjustment layer that allows you to convert your color images into black & white with a great deal of control and in a more user-friendly way than ever before.
With your photo of choice open, simply click on the "Create New Adjustment Layer" icon at the bottom of the Layers Palette and select "Black & White." This will open the Black and White dialog box which will allow you to adjust the influence of the reds, yellows, greens, cyans, blues, and magentas in the resulting b&w image and to set the hue and saturation of an optional tint.
However, this process can be filled with a lot of trial and error as you adjust the individual sliders. It's not always clear which areas of the image will be affected by a given slider. One of the options I particularly enjoy in Lightroom is the ability to view a before and after of my photo so I can see where the blues are located and I'll have a better idea of how I need to mix the levels of each color.
In CS3 - or in earlier versions of PS if you use the Channel Mixer to convert to b&w - a good first step is to make a duplicate of your image ("Image>Duplicate" and click "OK") to have open alongside the one you will be adjusting. That way, you will have a similar before and after view of your photo and will be able to work through your conversion process with more precision and more quickly.
Note: Under "Image>Adjustments" you will also find the "Black & White" adjustment. However, as with all adjustments, flexibility and being non-destructive are key. So in order to preserve your original and to continually be able to tweak your settings, try to use an adjustment layer whenever possible when working with your images.