Adam, I can totally relate. I used to be in great shape, was in the infantry in the US Army, did Judo/Jiu Jitsu 5 times a week, and lifted wieghts. I left the army, hurt my back and knee, and took a desk job, and put on a ton of weight. Even then I felt strong, since I know how to use my weight to power myself around when needed.

A year ago, tired of my wieght, I went to the gym again. I was cleared by my doctor, but was warned to take it easy and build up to an intense workout. I was also doing a LF diet. I figured I was still strong and did not follow my doctor's advice. I almost passed out doing cardio, pulled a couple muscles and inflamed my chest wall pushing wieghts, and ended up back on my butt gaining more weight.

I started working out recently, while following the LC WOE. This time though, I took it easy, got some advice from a good friend of mine that is a trainer, and it's going a lot better. I am still in the ramp up stages, but I feel a lot better and I have not hurt myself. As I start increasing my workouts I plan to increase carbs some, to help my weight training.

A couple suggestions- Getting a personal trainer is a good idea. Your skinny, in shape friend probably has NO idea what sort of workout you should be doing. If nothing else, pay for a couple sessions, just to get you started. If that is not possible I suggest doing this-

Start easy. Get on a bike or treadmill, or elliptical training and go easy for 10-15 minutes, take a break, and do it again for 10-15 minutes. Get your body used to moving. Don't worry about wieghts right now. Before someone can do weights or high intensity workouts, they have be at a basic level of fitness, something your not at right now. Trust me I know all about that. If you feel dizzy or light headed, stop. Take a break, walk around slowly and relax. When you feel better, carefully continue to do basic cardio. For now, just get used to moving.
You will find it easier and easier to do a light workout the more you do it. You will know when to increase time/distance/resistance and increase you work load.

Gyms can be very dangerous for people that are completely out of shape (like me.) When you walk into a gym and see healthy people working out in a seemingly effortless manner, it can put a person into a dangerous mindset of excessive expectations. We have to get healthy before we can do a lot of things a healthy person does as routine.

Remember, fitness is as gradual a process as weightloss. If you take a slow and steady approach to fitness, with time you will be able to bench 200+lbs with ease. Just do it slow!