I tried to add the sound to an existing silent movie by 1)Load movie---but this, when I tried to see it: "An error occurred inside a plug-in contained on this page" although KM didn't crash.

-> Was the sound in the form of a .swf file? If not, enter the sound file in the sound section on Movie > Sounds and Actions. Load Movie is only for .swf files (no extension checking is done at this time).

While I'm asking all this, I might as well add: What do you people mean by "daisy-chaining" little short movies together?

-> What I meant was that you can string movies together by using load movie on the last frame of one movie to load the next movie. This allows you to play very long animations because streaming will help you out. Correct me if I am wrong, Johnie.