When resizing your stills you just need to need to key on the vertical size and let the horizontal be whatever it happens to be to keep the same aspect ratio. For example, a “landscape” photo may be sized to 720×480 or 640×480 depending on the aspect ratio, and a “portrait” photo might only be 320×480 (width x height).
As mentioned before, if you’re not zooming in, aim for a height of 480. To zoom in, ideally you would want the height of the visible portion to be 480 at the maximum zoom point. In most cases doubling it to 960 is a good size to use, but if you need to zoom in really tight you’ll want a higher resolution.
-Jim