I do agree with the others that 6 months or even a year isn't a realistic about to time to lose what you need, in a healthy way. Putting dates for achieving our goals can sometimes discourage us if we don't hit them. As long as you eat healthy, excerise, and stick with it, the weight will come off.
1-2 pounds of weightloss a week is a healthy amount to shoot for but starting out, you will prob lose more then that. When it slows don't, don't get discouraged.
You need to figure out how many calories you need to be eating to lose weight. Theres a calorie calculater here: http://caloriecount.about.com/cc/calories-goal.php
that should give you a general idea. Make sure to adjust your calorie amount as you keep losing.
Pictures and measurements, and trying on clothes that were what you wore at your highest weight are great ways to keep track of your progress if your getting a little frustrated. It won't be as noticable at first but the more you lose, the smaller about of weightloss it takes, to see a difference...
It took me 4 years to shead 170 pounds, with plenty of breaks in that time frame of maintaining until my modivation kicked in again. Be persistant. Because you got this.
OH excerise...make sure you SWEAT...get that heart pumping. Mix up what your doing and when something becomes easy, make it more challenging. Excerise goals are a great way to keep you sticking with it...