I see someone mentioned "Crossfit.com" because it is a great Grassroots work out program, though starting out trying to do crossfit is imtidating, it can be scaled back and work fine. Crossfit is kind of the anti-Gym type work-out, as grassroots as it comes. (I have been training to do the 300 work out by my birthday. I'll be 45 this year.)
The number one thing is to completely change your attitude about fitness. The gym is not your enemy. I completely understand not liking the gym when you are wanting to get back into shape. I hated going to the gym and feeling like the weight bench guys were there solely to laugh at my progress, until the day when I was able to do 50 lb Kettlebell swings and then they kept their smirks to themselves. (My wife also works out and can lift more than me...after doing a 100 set-ups with a weight plate on her chest...the gym rats run to the shower when she shows up,) Perserverence. When I feel embaressed at the gym, I just imagine how much better I will be doing next year and keep at it. I use the same philosophy as I do when I ride sport bikes, I look thru the curve to where i want to be instead of where I am at. I get completely in the "me" zone. It is something I am doing for me so that I will feel better, look better and not regretting what I did with my life when I am sucking on tubes and pooping in bags at the old folks classic alt. rock night at the Senior center when I am 75.
My wife uses a book that I started stealing work-out schedules from, (and being in tip top shape and able to run a solid 6:00 minute mile 10K,) I found the work outs to be very good and versitile, the book is called " The new rules of lifting, lift like a man look like a godess"...I know the title sucks, but the work outs are great. The book is written by Lou Shueller who writes for Men's Health magazine, my wife says he wrote a book for men, (probably a couple) but me being a tight wad just reads her book and was shocked how good it was. Tons of good information about getting in shape and staying there. You will not regret reading the book.
Diet. No more beer, soda or fatty snacks. I work a swing shift of twelve hour shifts at a steel mill, no one is more tempted than me to grab a Mt. Dew at 3:00 AM to stay awake, but I absolutly know that a soda habit means weight gain and a bad dieting habit...Mt. Dew leads to Milky Way(s). Discipline. Tupperware containers, Broccoli and Califlower. Water and coffee.
I subscribe to Muscle and Fitness magazine, though it features ridiculous steroid models, there is a ton of good information in it about fitness and dieting..just scale back their weight about 70%. (I do anyway.)
I run... a lot...but running or walking will not cause you to lose weight...I have seen plenty of obese people run for hours on treadmills. You have to change your heart rate while you run, up hll, down hill, outside.
Sign up for a 10K. Decide that you do not want to be the last person across that line. Buy an Ipod, (stimulating the economy while you do,) and go out and have a good time.