First of all, don't compare yourself with your Curves friend. Each person is different in size and the body structure. Visit your doctor and talk to him/her about a diet plan that is right for you and the amount of exercise you should be doing for your current cardiac condition. Thirty pounds may take 6 months or more so don't be discouraged or expect a quick weight loss. Losing the weight slowly will be easier to maintain later on and watching what you eat will be a lifestyle, not a diet.
First count the calories that you currently eat and set a goal to eat less and burn off about 1300 per week in combination. For example, if you currently eat 1600 per day, try to eat 700 calories less and burn off 600 calories at the gym per week. That would be 100 calories less per day (700 calories) and 3 trips to the gym at 200 calories each trip (600 calories).
Avoid sugary drinks (lots of hidden calories) and go for diet drinks. Use sweetner (I like Splenda) instead of sugar. Measure your portion sizes (that's my problem!) and read up on how much portion sizes really should be. Keep eating out to no more than twice per week. If you overeat one day, then make it up by doing more at the gym, but try to keep within your daily calorie allowance. Write down what you eat and your gym activities so you can be accountable to yourself.
Try moderate weight lifting. Don't worry about building those awful looking muscles that you see in body-builder magazines. Women just aren't genetically going to look like that! But do add some weights into your routine. Slowly increase the amount of weight and try to do 15 repetitions for 2 sets of each body part. It's best to get with a trainer until you understand the best ways to go about weight lifting. This will not only strengthen bones, but will also help with weight loss and toning (you'll burn calories in your sleep!).
Weight loss is a journey and you should find something you enjoy doing along the way. Once you have reached your goal, continue to monitor your calorie intake. You should know at that point how many calories your body will need daily to maintain your weight.
Most importantly, don't follow fad diets or take pills! Remember that weight loss and maintenance is a lifetime commitment - not a quick fix plan of weird foods that you won't eat in the long run. There is no magic plan: it is all based on "calories in - calories out". It's really a simple concept that people try to make difficult so they can write books/CDs etc. to make money. Just remember: calories in - calories out. Good luck!!!