gryffnn is correct. DV, as well as other professional video formats, uses rectangular pixels instead ot the square ones used for computer work.

Therefore, unless you're using software that specifically compensates for that (like Lightwave) your best bet is to render at 720 x 540. You can take that into FCP and resize it to 720 x 480. It'll look funny but render correctly if you're outputting to DV.

If you use FCP to output one of the computer-sized movies (320 x 240 for example) it should compensate and render correctly.

Also, that 720 x 540 includes a "safe area" that's designed to compensate for TVs being offset (non-technical description). The safe area is actually 640 x 480 and centered within the 720 x 540 area. When you frame your shots it's good to keep this in mind.

I use something like the image above as a background image when setting up my shots in Poser. My safe area is inside the green. My visible screen is divided into thirds so I can follow the thirds rule when setting up the shot. I change the color to suit my convenience but you can see the general principal.

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