Actually don't think you can render a quicktime dv, but rather to quicktime using dv template specs, which would limit you to 4:3. Choose another option in the custom dialog after selecting render as -> Qtime mov. Should be able to choose custom, and any frame size you want, but watch the pixel aspect ration to make sure you are consistant (may not want to render a 1:1 pixel ratio proj as .9 or the reverse) as this might effect your final results.