I do relatively low weight, 100 lbs on bench press, 55 on curls and military presses, sets of 15 with no or minimal resting between sets. It's an add to the walking.)
Condition, condition, condition. I will get this done.
Just a few comments on conditioning:
Realistically, if one's doing everything right, one can lose up to about 2.5lbs/wk. That ought to get you to 235-240ish. You could get lower than that if you starve yourself and run yourself into the ground, but that'll be counterproductive, unsustainable, and not altogether healthy, especially for a big dude who hasn't been exercising regularly (btw, a physical exam and running your exercise regime past a physician wouldn't be a bad idea). I think you'd do much better being in good condition at 240, than being starved and weak at 200ish.
To lose that 2.5/wk, you'll need to watch your diet ("calories in") - healthy food (and no junk food), limit your snacking and booze, eat regularly, plenty of water, etc. You'll also need to boost your "calories out". There are manifold benefits to resistance training, and you ought to keep doing it, but lifting weights for an hour a few times a week burns barely more calories than baseline. I see plenty of guys who've been going to the gym to lift regularly who can still stand to lose quite a bit of weight. Walking is good (I make sure I get plenty of it in), but consider getting on something like an elliptical trainer a few times a week, and keep a brisk pace to get your heart rate up (again, a physician's ok would be a really good idea).
And on the subject of weight lifting - if I in your shoes, I'd skip the isolation exercises like bench/military press and curls and do compound exercises. Squats, deadlifts, kettlebell swings, burpees, etc all use multiple muscle groups and you'll get much more bang for your buck.