What I found to work for me is very simple - walking.
The machines in my gym can monitor your heart rate when you hold the grips. Calculate your max heart rate - a rough calc I think is 240 - (age *2) and find a rate of exercise that will get you to 65-70% of that. I'm 26 so what I aim for is a heart rate of 125-130 or so - thats a brisk walk at 7.5km/h for me. 30 minutes of that and I've burnt off about 400 calories.
If your exercise is more stressful than this, you're probably burning up carbs/protein rather than fat.
For cardio work, I also do a further 15 minutes on a cross-trainer and about 10 minutes rowing. But it's the walking that burns off the fat, trust me. Just make sure it's a good quick pace.
You will have to be more disciplined about your eating, but not to the point of eating rabbit food three times a day. Everything in moderation, especially beer.