Pedometers are a great idea and walking is the best fat burning exercise of all - certainly the easiest to build into your daily routine without a trip to the gym or getting changed for a run.
Remember, though, that whilst you'll be burning calories with each step you take, unless you walk for more than a few minutes, you'll be mostly burning carbs, not fat.
To burn significant amounts of body fat you need to walk at a steady (brisk) pace for around 20-30 minutes in one go. More if you have the time. You'll burn 100 calories a mile (more the heavier you are) of which around 70%+ will come from body fat.
As Maleficent stated, 2,500 steps in a mile - do 10k a day and that's around 400 calories (approx 300 fat calories). Whatsmore, your, metabolism will gradually return to normal after the walk, meaning that you'll continue to burn extra calories for an hour or two afterwards.
Say you burn an extra 500 calories a day doing your 10k steps. There are 3,500 calories in 1lb of fat. 7x500 calories is 1lb of weight loss a week. 52lbs in a year. Combine that with eating 500 calories a day less than you need and you could be looking at 2lbs a week or 104lbs in a year. Soon adds up!
All the best,
Marcus