I agree with Sonnofa, Dr. Atkins New Diet Revolution is probably the best book for people just starting to lowcarb. I also found the discussion in Protein Power (by the Eades) very useful in understanding why lowcarb works. Atkins for Life is more geared toward maintenance.

If you have not done so already, you might want to check out the Triple Digits Club which is the special area of the forum for people with over 100 pounds to lose. It is about mid-way down on the forum homepage.