I have an eliptical machine (I'd love to run, but I live in Seattle, and its cold and wet). I use it between 40 and 60 minutes a day. I highly recomend it. Your gym probably has one. You don't need to do it as long as I do, but you can burn the same amount of calories that way as walking on a treadmill but it will take about a quarter of the time.
Here's a good calculator to figure out roughly how many calories you lose in a day. Just estimate the time you spend doing each activity (it includes all kinds of exercises, sports, and other activities, like sleeping and reading): http://www.healthstatus.com/calculate/cbc
There's pretty much a healthy alternative to every junkfood. Try eating a sandwich without mayonaise and cheese. Or gardenburgers or boca products instead of cheeseburgers. Theyre really not that bad. Sorbet is a non-fat alternative to icecream, and its quite tasty. Instead of potato chips r frenchfries as your side dish, try a salad. Once you get used to eating these alternatives to junkfood, you barely think about it. You just need to be motivated to force yourself to do it. Keep coming to message boards like this. Keep talking about it to as many people as you can. Keep the idea of weight loss fresh in your mind.
I get easily deterred if I don't keep my diet and exercise plan in mind, i find myself instinctively eating when I'm not that hungry.
Another trick my girlfriend showed me is to make a half cup of popcorn (no butter) and eat that, and drink 2 or 3 glasses of water. It makes you feel extremely full. I haven't done it, but I might try it if i felt inclined. Just force yourself to eat healthy food your not craving, until youre full and not thinking about your craving anymore.