When I was in labor with my last my outer os was dilating but not the inner os, the nurse told me to keep walking and the pressure from baby's head will help dilate me. After walking laps for only a half hour my contractions were more effective and the inner os did begin dilating. So for me the walking during labor helped a lot.
Unless your body, and your baby are ready to come NOTHING will help you go into labour. Walking helps because it's keeping you active and gravity is giving things a helping hand. It prepares your body physically in a way, but won't actually make you go into labour. it's still worth doing though - better than lying about and having all your bones and muscles tensing up and not being used.
If you're already in labour, walking is supposed to help because a) gravity is playing a part in helping baby down the birth canal and b) it actually makes your contractions easier to deal with. It's the best thing to stay as active as you can during labour. Laying on your back the whole time just slows it down, and often, is actually much more painful.
I felt like it did, or it at least it got me doing something so my mind wasn't completely on what I was feeling. The nurse at the hospital told me it doesn't really make a difference though.