here is an old link to my previous post: https://discussions.apple.com/thread/3012685?answerId=15056178022#15056178022
in the above link, there was mentioning of creating iweb widgets...
well, the boat had left the dock, the train had left the station... very few people sent in feedback and asked for tools to build iweb widgets - gurus and experts included.
adding scriptaculous's effect.js library to my page is just drag/drop the (my) wdiget from widgets pane into the page.
however, you can add it to your page using html snippet widget (sorry, no more instruction in this forum).
as far as post editing... that's iweb1 method (that's 5yrs ago!!!) when there is no way to add code to iweb page (no html snippet widget).