Click the Walking to Disney clippie in my sig. It will take you to the thread that started it all.
Basically - calculate the distance from your home to a destination in WDW (resorts are easiest) using MapQuest, or other online mapping service
Set a goal of walking the distance to WDW in a determined amount of time. The original premise was to cover the distance by the time of your next visit ... not realistic for everyone.
You can walk around your neighborhood, at the mall, on a treadmill, wherever. There aren't any rules about what steps count. I used to only count the walking that was in excess of my everyday steps here and there. Now I wear my pedometer all day and count every step.
I figured I could average 2 miles a day without a lot of effort, therefore it should take me until the end of July 2006 to reach Magic Kingdom.