I think it really depends on a lot of things.
If you are burning more calories than usual, then yes, you can lose weight through walking. But if you are going from more intense exercise to a style of walking that burns fewer calories, then I'd say no.
To get the most out of walking, I think you need to incorporate some race-walking techniques, which will allow for faster speeds (I got up to 4.85 mph walking my own 5K this past summer, and this coming summer, once my 'walking season' kicks in, I intend to go for 5 mph). Once you can walk at a sustained pace that is fast enough that your body would rather run, you are burning even more calories than running the same pace, because your body is working ineffeciently, and using more muscle than running does.
I found several books to be helpful:
"Walking Fast" by Therese Iknoian
http://www.amazon.com/gp/product/0880116617
"The Complete Guide to Marathon Walking" by Dave McGovern
http://www.amazon.com/gp/product/0966217624
"Race Walk Like a Champion" (book and DVD showing techniques):
http://www.racewalk.com/Shop/RWLCBook.asp
All of these books give training programs as well as form pointers.
You can also find free info on the web on race walking technique (just do a search under that term).
The important points are:
Arm swing : bend arms at about a 90 degree angle or a bit looser, and swing them forward and back, not crossing the center line of the body.
Heel strike/foot roll/push off : when stepping, hit the ground with your heel, with toes pulled back, then roll through the sole and try to keep the foot down until you can push off the big toe.
Hip movement (this is the part that can look funny! but many people misinterpret it as a 'roll' from side to side) : this movement should be a forward/back movement, with as little side-to-side movement as possible. All your energy is directed forward for best speed.
You can work on each of these elements separately (on different walks, or on different legs of the same walk) until they start to feel more natural.
I find it also helps to have a bit of competition. I competed mostly against myself, getting a Garmin Forerunner (wrist-mounted GPS) to track my mileage and speed, and trying to improve as the season went on. I also would have unofficial 'races' with other people I came across while walking, trying to pass the person who was 1/2 a block ahead of me, and so on!
I absolutely cannot run, or my knees will give me problems, but I can walk faster than some people run (I've passed some joggers!), and the only problems I've had were some 'breaking in' aches (sore shins at first, from the toe position, and one day, a couple of black toes, one of which eventually lost a toenail, because I was on a long walk, and had neglected to trim my toenails enough, and they kept hitting the ends of my shoes).
I personally walk without music (I can make enough 'noise' in my own head to compensate, LOL!), because I know I would automatically follow the beat, and I couldn't find any walking tapes that were fast enough (so they would actually slow me down rather than help me speed up). (I also like to hear what is going on around me, and there were several times during my walks that I was glad I wasn't distracted by music). I think, though, that if you are not walking as fast, music could help you keep a steady pace, and push yourself at times. I used to walk to music, and would make my own compilation tapes (yes, tapes, it was that long ago!) using my own music, which I'd timed to see approximately how many bpm there were in the songs I liked, then combine them in a tape to have a warm-up, then gradually faster songs, then a cool-down.
