[fablephil]"...can the z1 downconvert for playback? "
Most HDV cameras can downconvert. Double-check in your camera manual.
However.... don't expect to shoot 24p with the Z1 and have it look right. Sony screwed the pooch when it came up with the Cineframe mode for the Z1. It is unlike any other faux-film-look mode on the planet, and is not even worth messing with. Use it at your peril. You've been warned.
Sony wised up, and corrected Cineframe on subsequent HDV cameras, the X1 among them.