I just want to mention that many mothers, myself included, find that logical and natural consequences are far more effective, in the long run, than arbitrary punishment. I could go on for days about these things, and have, but I would really like to suggest a second book for you and very much hope you're willing to check it out.
Kids Are Worth It! by Barbara Coloroso.
I have a degree in child development, worked as a teacher for years, and read parts of this book with my mouth hanging open. It lit so many light bulbs and made me realize so much as a parent that I now tell everyone about it. An alternative is "Unconditional Parenting" by Alfie Kohn (I think that's right). I've been told it's strikingly similar.
What it comes down to is that good discipline is teaching and that behavior modification (arbitrary reward and punishment) actually involves very little actual teaching. The books explain it so much better!