Here is the problem: if Media Shout doesn’t understand non-square pixels and you give it a file that uses a PAR of 1.3333 it is going to display it as if the PAR is 1.0000 and the image will look vertically squished. This is why I suggested that you give it a format with a PAR of 1.0000. That way it can’t get the PAR wrong.
Having said that, it also might not be smart enough to handle widescreen ANYTHING, in which case rendering 1280x720p is not going to work either. This is why you have to ask the person who has the software or send them test files to see what the software does with it. That’s why I made the suggestion to render 4:3 video with the letterbox already added. This would be foolproof and you would be guaranteed to get letterboxed video.
You really need to talk with person who owns the software and ask them what format looks best, then render to that format.
~jr
http://www.johnrofrano.com
http://www.vasst.com