Here's my household advice for what it is worth. Cut the carbs, up the veggies and don't eat after 6 p.m. Walk at least 5 days a week for 45 minutes to start and work on your abs daily. Make sure your ab exercises are done correctly. Most people do them wrong (use back muscles instead) and they are very ineffectual. A partner can really help here. My training partner actually used to "feel" my abs to make sure they were contracting. You will need to work all areas of your abs (upper, lower and obliques). You will be able to tell you've done it when you're a little sore for a couple days.
After a couple weeks, you need to walk for 30 minutes and add resistance training. A set of light weights can help. You might try tai chi or pilates (bellydancing is a good workout) to give you some variety. Check with the campus rec center (local YMCA maybe?). You might be surprised to find a community ed class or two. Water aerobics is a great workout if your school offers it.