yeah, swimming might be a good way to begin, it's much easier on the joints.

you could also try a yoga for beginner's video tape. lots of relaxed stretching and breathing. if they do something that's not comfortable on your foot, try to find an alternate move that will accomplish the same thing.

i luuuuuve my yoga. ok, it's not burning too many calories here, but it's better than nothing. and all the stretching i think does have a toning effect. it's a start for me, and i'm incredibly lazy.