the first week like on any diet is usually pretty impressive, you could lose 7lb. I think I lost about 5 but I was already doing a different diet. After that anything goes, I have some weeks where I lose 4 or 5lbs then others where I lose little. I have stalled this last month due to me eating carbohydrates - but thats not a bad thing in my book ... catching my breath and actually showing me my limits for when its time to maintain.
good luck, you will enjoy atkins it doesnt feel like you are on a diet most days.