I found that walking, once you're used to it, doesn't burn a lot of calories. I also found that it doesn't make you better prepared for running!
I really hate running, a couple of years back, I really wanted to get into being more social and fitter, I joined a rugby club and a gym when they were starting pre season training. I lost about 25lbs from using the gym 4 times a week and doing rugby drills 2 times a week in about 3 weeks.
During a rugby training session, I planted my foot wrong and tore the meniscus in my left knee. I was told by an NHS physio after surgery to not play rugby anymore and that running is probably a bad idea. This made me pretty damn depressed, thinking of how I was doing well beforehand only to have that happen. Then I thought '******* the NHS', started back at the gym near my work, strengthening my knees, cycling (in the gym) and doing freeweights and then ended up being made redundant. So all of the good work went to waste and I gained back the weight from feeling pretty awful and then getting a job which was a 4 hour round trip (it's only 14miles though, public transport to it is real slow).
2 Weeks ago, I moved to the town my work is in, I'm cycling into work and have covered 60km since last Monday. I've found that my body is getting stronger and it's really enjoyable. I've only lost 1lb in my first week, and doubt I've lost anything this week either (with my birthday and 2 meals out), but I feel fitter than when I moved.
I'm going to aim to do 150km a month on a bike to see if that will do anything to help me lose weight, if I'm on flat land and my legs are spinning most of the time rather than cranking up a hill, then I think it will be better for weight loss, my legs feel 'thicker' from cranking up hills, so my legs are getting more powerful it seems.
I've also found that I can be careful with what I eat, lose a lot in the first week but then lose nothing if I'm doing no exercise and that gets me down. I definitely feel better if I'm exercising. Even if I lose little or no weight, I feel fitter and don't get bogged down.
I also noticed a plan 'couch 2 5k' which looks quite interesting, it's supposed to ease you into running, doing 60 seconds of running to 90 second breaks. You do 3 sessions a week, and should build your stamina over several weeks rather than stepping outside and trying to run or jog for 15 minutes straight, which is hard if you're heavy and not used to it.