There are lots of ways to convert a color image to black and white in Photoshop. Some people use the channel mixer, more advanced users may bring each of the RGB channels into their own layer and use masks. Various plugins and actions are available to simulate different looks.
I was catching up on excellent Photoshop Workbench tutorials over on The Radiant Vista this morning. About half way into the March 22nd episode my jaw hit the ground. Photoshop CS3 has an amazing black and white conversion tool — the new Black and White adjustment layer. The BW layer gives you individual luminosity control over the colors RGB and CMY. You can either use the sliders in the dialog box, or just hover over the area you want to brighten or darken.
If you’re a fan of using a Selective Color layer for color images, this approach will quite intuitive. Kiss the Channel Mixer conversions goodbye folks, the Black and White adjustment layer rocks. If you’re short on time, jump about 9 minutes into Mark Johnson’s Photoshop Workbench episode to check it out.