Yeah, definitely check with your doctor first, but one of the most important things is to start moderating your portions. Try a whole grain cereal and lo fat or soy milk for breakfast and lean Cuisine entrees for lunch and dinner for a week with a piece of fruit and/or nuts to snack on in between meals. L/C meals are packaged to give you a healthy, tasty, nutritionally balanced, and properly sized portion. There's a ton of em, so you don't have to eat the same thing over and over.
From there, start an exercise program--something you like and can stick with, but don't forget to put in some variety so your body doesn't get "too good" at it (making the body react differently is where the biggest losses come; if you do the same thing every day, your body will find the most efficient way to do it so it doesn't have to work as hard).
For more inspirational and sound advice, go to www.sparkpeople.com. It's very encouraging and free!