Congratulations on your pregnancy!!!
I'd say eat as you always have on Atkins, but add a couple servings of fruit and extra vegetables and some dairy (calcium is really important!). If you can handle it, a serving of something whole grain every day or two or three would be fine too. Instead of *normal* whole grain items, I try and use low-carb/whole grain items like low-carb bread (there's that 45 calorie and delightful stuff), low-carb wraps (by Flatout, they're by bread or by the deli in your grocery store), low-carb tortillas (I like Mama Lupe's - if you can't find them by you you can order them from Netrition.com). I also use more beans on my salads and in soup.
You don't need any extra calories right now, not until your second trimester. I know, easier said than done.
I was STARVING when I first got pregnant and definitely ate more, but I made a strong effort to eat as healthy as I could. Though I was dieting before I got pregnant (as you were), so I did actually up my calories some because I didn't want to be in weight loss mode anymore... So you'll probably need a couple hundred more than you were eating while dieting. Whatever stops you from losing weight, but doesn't make you start gaining either.
Weeks 5-9 were the worst for me because I was so exhausted and nothing appealed to me. A lot of women experience morning sickness during this time, too (thank God I didn't). This is when you'll find it hardest to eat right, but after that hurdle it's pretty easy to jump back to it. Be as healthy as you can, but if you're puking your guts up and the only thing that appeals to you is cereal, it's better to eat that than nothing at all...
Are you able to keep snacks at work? I have a drawer of just snacks... In it I keep pumpkin seeds or almonds (or some sort of nut/seed), a jar of natural peanut butter, fruit cups (no sugar added if you can find them), little cans of V8, and sometimes some dried fruit. I also keep string cheese in the fridge of our breakroom. I'll also bring fresh veggies and ranch dressing with me to snack on in the afternoon sometimes, depending on how big of a lunch I ate. The key is to keep a variety of snacks so that if you're in that mindset where only certain things appeal to you, you're bound to have
something that sounds good to eat! That helps you avoid the vending machine (if there's one nearby).
I can honestly say that my regular snacking/eating is why I never got morning sickness. I did occasionally get a little nauseous, but if I ate something I would feel better. I know this isn't the case for a lot of women, but it definitely helped me out!
Oh, and don't forget your Prenatal multivitamin!