I say use as much dynamic content as you can. It offers flexibility and and makes updating way easier in the end.

That mean.. images should be loaded externally using loadMovie();

I also make each 'page' (section) of my web site an external.swf and load it in using loadMovie() as well...

my MAIN.swf is somewhat just a SHELL, with my navigation, some minor layout stuff/graphics, logo..footer..etc.. and the main content section(s) are empty/blank movieClips that just sits there waiting to get content loaded into them