I am no expert, but this is what I have gathered from reading Health Magazines...

Walking is an aerobic exercise and will do nothing for skin. You need a muscle exercise program.

To help reduce excess skin you need to do muscle exercises, that will 'tone' you by tightening the skin.

You can do these at home.

http://www.weightlossforgood.co.uk/exercise_at_home.htm
has some good stomach exercises if you can't do a crunch (without cheating and using your neck - BAD!).

I find these really help.

Apparently, for excess skin the best is to use heavier weights with fewer reps. Build up to this.

If you don't have free weights and want to do the arm exercises for a temporary move I use 3L milk bottles that I gradually fill up with more water. Just find somebody who still drinks Milk though I guess!!

From what I have read, it seems to be very important to do these NOW. It is easier to lose the skin as you lose the weight then to lose it afterwards.

The website I have linked to isn't the best in the world... but on google all I can get is advertsing!! I know there is a really good website I looked at a few months ago that had PICTURES and more safety information... but I can't find it!!!
Anyway, if you are going to go this track there has to be something more on google!