If you get a decent treadmill, they have good floating floors. It
basically cushions the blow of your weight when running. If you
really cant take it anymore, the elliptical will do it for you. Its
lower impact to the body and gets your arms in the game too. You can
get just as good as a workout with ellipicals as you can with running.
Stay away from stairmasters if you already have problems. Nothing
like doing some damage to those already worn knees.
Get a good unit if you want something that will last you for awhile.
(depending on your desired routing)
>> Stay informed about: Equipment Alternative to Running