Hello mate and welcome to the forum
I am 5 feet 10 and started out at 19 and a half stone (about 124 kg) so where you are now and where I began aren't a million miles away.
I was determined to do something too, and over time have done the following:
1. Stopped drinking alcohol (lots of empty calories there).
2. Weight training 3 times a week.
3. Cardio 5 times a week.
4. Completely revised my diet, both what I am eating and how much.
As of my last weight in I am 14 and a half stone (about 92 kg), although obviously this has taken some time. I have lost, and continue to lose, around 2 pounds per week by eating 2,000 calories a day or thereabouts.
Although it doesn't seem a lot, over your 18 month goal that would be 156 pounds, so over 11 stones, so your goals are certainly realistic.
Just accept each gradual loss as a step in the right direction, and don't be put off by odd weeks when you don't lose. They will happen. Also, as you get more into working out, don't get too hung up on the scale weight. Go by how you feel, how your clothes fit, have you had to tighten your belt another notch...that kind of thing. This is because you will get to a point where the scale isn't moving much, but your shape is changing. This is a good thing.
Good luck!! I know a bit about the journey you are about to begin with losing weight, as do many others on here. It can be done and it sounds like your mindset is just right :)
<message edited by ian1969uk on 11 November 2009 17:04>