paradox saidsfb987, you might want to check out the blog of Dr. Michael Eades, who wrote the 'Protein Power' books. He covers the science of low-carb dieting in depth.
I wish the site was designed better but it does give useful information.
Hes the short end of what diets like atkins and southbeach do. First 1-2 weeks, depending on the diet, require you to cut out carbs. This is to shock your system and for a majority of the people it does and the results are 6-10lb in a week.
After that you increase carbs to the point of finding the sweet spot. This number varies depending on the person. It is basically the number in which you body uses it all for energy and does not store it, also so its enough that you feel full when eating.
The problem is like diver said you will put the weight back on if you go back to your usually eating. The best way to go about this is looking at what you eat and how much. The calculate calories of your workout and food intake and figure out what needs to be changed.