Not sure if you have access to one, but elliptical machines might be good also. The ones at our gym have a hand rail in front, and then two handles that move back and forth as you walk/run on the sides. The nice part about the elliptical is that your foot never leaves the tray it is in...the tray moves with the foot, so it is a very natural walkin/running motion, but you don't have to worry about your foot coming down awkwardly or slipping out from under you like it can on a treadmill. Also, if you stop walking, the elliptical stops moving...which makes it somewhat safer I think than a treadmill where you have to turn it off.

If you don't have access to one, go find one of those "free two week membership" deals from a local gym and go in and try one there. Just be prepared to resist a sales pitch trying to talk you into buying a membership if you aren't ready to do that.