Just thought I'd share with you my initial success with using a bit of software (for PC and MAC) called Perfect Diet Tracker, and also NIKE+ which some of you might be familiar with.
Perfect Diet Tracker has a 7 day trial so you can test whether its right for you. Essentially you put everything you eat and drink each day into it and it rolls back and tells you how many calories you've consumed. You start by putting your height and weight into it - and you'll gradually see a graph which tells you how far you've come...pretty good to visualise this stuff. Link is here: http://www.perfect-diet-tracker.com/
So that sorts out the diet. Nike+ sorts out the exercise. As you run (or in my case walk ), a sensor in your shoe tells your ipod nano how far, how fast, and how many calories you've burned off. Over time this builds up to give you a great view of what you've achieved....I've gone nearly 20kms in a week! http://nikeplus.nike.com
I think it really helps to actually see what you're eating and drinking, and to actually see how far you're walking/running. I'm finding it a real motivation and I hope it could help someone else too