If you are just going to make a movie and it won't be interactive then you could just make the whole thing in FCP and export it as an FLV file. Then you can just use Flash to play the video using either the media components or your own player if you want to make one.
You can export an FLV file right from FCP or you can use something like Sorenson Squeeze to create. The latter will give you much more control and better quality.
As for the average window size, its the same considerations as when you create an HTML webpage. I never go bigger than 800x600 for web stuff. And as for the video, the standard 4:3 size for the web is 320x240.
Hope this helps,
Lee
--------------------------------
http://www.leebrimelow.com
