5 lbs a week is possible, but it is the maximum of what a person should and can loose healthily. If I was you I would aim for 20 lbs, but not be too disappointed if you loose more like 10-15.

For diet, I think Happyjello pretty much covers everything I would want to say on that subject - however, I'd pay extra attention to portion control - compare your food intake to someone you know who is healthy and slim and use their portions as a guideline. As a general rule though I'd half your intake of carbs and meat and double your intake of fresh vegetables.
Also, as suggested, having an "anti diet" day once a week is a good idea (it keeps the cravings at bay), but as your goal is quite high I wouldn't go nuts on that day, perhaps keep it to one "crazy" meal on that day, or have a piece of your fav cheesecake, whatever, my point is choose your vice, don't eat all of them!

As you want to loose quite a lot of weight in a relatively short amount of time, I'd work out, you don't need to go to the gym, you can powerwalk or buy a fitness DVD. If you don't work out at the moment I'd build it up, start with 3x a week 30-45 mins (incl. warming up and cooling down) in week 1 and 2. Then move up to 4x a week in week 3 and 5x a week in week 4.

If you do work out already, mabye step ip up a little and change your routine to really get your body working.

And my last piece of advice - if you have an off day, don't stress out about it, just get back on the wagon te next day. And if you are having an off day or are feeling tired and don't feel like working out, try to do something, like maybe go for a walk for half an hour, quite often you feel much better after and you don't have to feel guilty about not doing anything.

Good luck!