In Photoshop go to adjustment>channel mixer and check monochrome, mix the channels in varying amounts until you achieve the look you want. Make sure the channels add up to 100%. Green usually has the most tone and detail. I have seen some other techniques by Russell Brown @ russellbrown.com and by Vincent Versace @ vincentversace.com. Vesace is really great I saw him at Photoshop World he is a classic BXW shooter like me and has come up with techniques in digtal that come really close to traditional black and white photography. He has a book coming out and several DVDs. Check him out. Russell Brown works for Adobe and is one of the geniuses behind Photoshop.