I think that in the beginning, many people are in denial about what got them to the weight they are at... I was one of those. You didn't just suddenly wake up at 300lbs one day. You need to critically evaluate what you are doing that has lead to this weight (obviously, overeating - but more specifically are you grazing on food all day, are you an emotional eater, do you just eat too much of the wrong thing, etc). You need to know why you are eating the way you are. You need to evaluate your lifestyle and identify your needs (for instance, I must be able to have convenient foods because I am not home alot), and then identify how you can make changes that still meet those needs but in a healthy way. I agree with the food journaling, that is something that gives you your true caloric intake, as most people underestimate the amount of calories they eat in a day if they don't journal. I think most people here use
http://www.fitday.com
As for exercise, there isn't any excuse for not exercising....find activities that you like that you can stick with; fit exercise into your day as much as possible; and set yourself up for success - I am a full-time college student, and have found that I must exercise before class or I won't do it, so I make sure I have a enough time to get in my exercise.
Make sure you set goals - but BE FLEXIBLE. Set goals that you are comfortable with and create a reward system that does not include food (for example, right now, my main goal is 50lbs lost, and my reward is a pedicure).
The biggest thing I can say is that you have to be truly motivated and ready to change your life. If you go back to your current eating habits, the weight will come back too... make changes that you will be able to live with for the rest of your life.
Good luck with your journey!