You obviously need to watch what you eat and drink - training is not enough. I read in the latest Men's Health that it might be a good idea to have a little something to eat before training as otherwise your body will look to the next most readily available source of energy which is muscles, not your gut. I think that's what it said. Here's a pretty good link: http://www.thefactsaboutfitness.com/
I would just stick with it - you cannot target a particular area for fat loss (fat loss will be distributed over you entire body). As your stomach has greater fat deposits it will take longer before you see the benefits. Exercises that target the stomach won't actually burn the fat from that area anymore than any other area but will tone the muscles. To reduce the fat; lots of vigourious exercise, a sensible diet and a bit of patience.
up hill walkin is deffo a winner !!!! try it on the tred mill 5 times a week and i guarentee youll see the difference in by the summer ( 2 months ) its rubbish doing it but force yerself for half an hour a day . good luck