If you don't want to gain muscle, it's very simple.. just don't eat more calories than you get in. You can lift all you want with however much weight, and you won't get bulky or anything as long as you're not getting the calories you need to "get big." Trust me, I tried for about 6 months working out all the time while getting plenty of protein - very minimal, if any muscle gain. I definetely got in better shape, no doubt about it, but no muscle gain.
So, basically, do plenty of weight lifting, plenty of cardio, and get about 30 mins of cardio in a day. Doesn't matter what the cardio is, just make sure it makes you sweat, and make sure you vary it. For instance, bike one day, run the next, eliptical machine the next, and so on. A safe rate to lose weight is to not exceed 2.5 pounds a week.
In terms of your diet, I'd probably try to hover around 1200-1300 calories in a day if I were you, while getting .7-1.2 grams of protein per pound of bodyweight per day.
In response to some of the above posts, there is no difference between bulk muscle and lean muscle in terms of how it's formed. It's all skeletal muscles, all the same. The only difference is the fat content you have. Also, fat will never turn into muscle, period. Fat does not store protein, which is basically what muscles are made of. Now, fat people might have plenty of muscle underneath the fat, but the fat never, ever gets turned into muscle.