I have a Dahon Espresso, which is the same frame as the jack as far as I know.

I have a topeak kiddie seat and hop off the train one stop early to pick up my son at preschool. My wife leaves the seat part there. Works like a champ. 40 pound kid, 7 mile ride.

Any rack that's not too exotic should work, as all racks that I've seen in the last 10 years seem to be pretty radically adjustable, unlike the old ones I used to put on my "10 speeds" in the '80's-- I never did figure out what that big spring clamp thing was for on those...