" I want to lose weight-now what?"

The problem with being on a "diet" is that it typically has an end-when you reach your goal weight. The problem with this is that a great deal of people then revert back to old habits and eventually end up gaining back their weight and then some. In order to make a tangible change in my life I had to first change my thinking. Instead of thinking of this as a "diet", I though of this as a lifestyle change with the end result being good health and the side effect being weight loss.
Weight loss is basically math- calories taken in vs. calories burned through exercise. I think that most people over estimate the number of calories they should be eating a day. In my Best.Links.Ever section I have included a link for the Mayo Clinic's calorie calculator. You just put in your age, height, weight (or goal weight), and activity level and it will tell you how many calories you need per day to maintain your weight. If you calculate this for your goal weight you will know where your daily calories need to eventually be.
The very first thing that I did (and I highly recommend this to you) was to start journaling everything I ate with a running total of calories.  I was shocked to see how many calories were in some foods and even more shocked to see what my total calories were. The journal also helped to show me which meals and which times of day that I was taking in the most calories. This is a great place to start. Once you get a baseline of how many calories you are taking in per day I suggest trying to cut out 500 calories a day (or burning 500 more calories) in order to loose one pound a week- a safe rate of loss. If cutting 500 calories is too daunting of a task then I suggest cutting 250 calories and burning 250 extra calories through exercise.
A word of caution here: Do not try to change everything a once. At the start of any new "program" people are always so motivated and immediately try to break all bad habits at once only to get discouraged and quit. My advice to you is to address one thing at a time. I found that I was better able to stay on course and I was more successful when I only had to focus on one life change at a time. Each week decide what you will work on that week and make a goal for yourself. If at the end of the week you don't feel that you have mastered it, then continue it the next week until you feel comfortable enough to switch your focus onto the next area while maintaining the one you have mastered. The goal doesn't have to be difficult. One of my first goals was just to drink 64 oz of water everyday.
One more thing to keep in mind as you get started: The beginning of any new change/program/lifestyle is always the hardest. IT DOES GET EASIER. I promise. You just have to stay the course. Keep in mind that it will be difficult and then believe that you can do it. My favorite quote is from Henry Ford. It basically says that whether you believe you can do something or you believe that you can't- either way you are right.