For the HD content, the only issues are the conversion from HD to SD... you'll need to scale or "downrez" it to standard def (720x480 is NTSC standard). The way we handle it is to output the edited scene once as an HD AVI, and then scale that to a master SD AVI. The SD AVI is what we use to encode all the different formats we need, Flash/WM/Quicktime/whatever.

Once you have your final source media, if you use Squeeze or Procoder, you can then just stack up whatever formats, bitrates, sizes you want and it will merrily go off and create all the different versions for you.