DPI!!! My head's going to explode! (Please, never mention "DPI" and "resolution" in the same breath again or my heart will fail.)
720 X 405 will work fine (better than fine) if you're doing an animation. 1200 X 800 looks pretty good on a computer screen. 2000 X 1600 will look great in any magazine or 8X10 print, (we use it for posters!)
p.s. Quick, Robert, jump in front and block me with your body when the next guy brings up megapixel render settings.