I'd recommend getting a physical first to ensure that your heart is ok.
I've worked out with weights since I was 18, (47 now) and have been a trainer and member in alot of gyms. Gyms are fine if you can motivate yourself to get there. But, as stated alot of people sign up and quit going after the first 2 mos. You've got to dedicate yourself and stick to it. Last fall, I was in a workout slump and "bit" on an infomerical - P90X. It's been a challenging, butt kicking workout that's gotten me into great shape. And, you do it in your home or hotel room. Basically, you need a DVD player and some space. It's alot of pushups, pullups, and fun cardio. You follow along to the DVD and there's a coach and students doing the same exercises that you do. It's motivational. If you get tired and can't keep up at first (and you will), then you hit "pause", catch your breath and re-start. I do NOT recommend P90X to you though, if you haven't been working out (Your work doesn't count!) at least moderately for some time. It is a very challenging workout. However, go to Beachbody.com and check out "P90/Power 90". It's a more moderate form of the workout that I'm doing.
Whatever, you do...take it slow and steady. If you don't do P90, start by walking every day if you can. Start out walking 1/2 mile and increase it every week or so. Your "lose 50lbs goal" is noble, but is going to be a challenge (especially coupled with stopping smoking). The other factor is diet. You can't workout and eat Big Macs. Traveling and eating correctly is especially challenging. Try to eat "clean" six days and week and allow yourself 1 cheat day where you can eat anything. Most people, myself included can't eat clean 7 days a week for long. "The pizza and wings start talking to us". So 1 time/week, eat that pizza and wings, BUT the next 6 days - clean it up!Good luck and stick to it. Do some form of exercise every day if you can and you'll get into shape.
Kyle