If you look back again at Graham Bird's 'tutorial', in the view you'll
see an example of the $option['update'] option, I agree it's difficult
know from the documentation that you are supposed to remove the $option
and stick it in an array....

        print $ajax->link('Delete', 'delete/' . $item['id'],
array('update'=>'tasks_done'));

If you want to do it on load of the page you'll probably need an onload
event attached to the body tag.

This should call a function which (if you want to have it cakeified)
should maybe have one blocks of code for each div you want to update:

                        echo $ajax->remoteFunction(
                        array("url"=>"/controller/action/",
                                  "update"=>"divToUpdate",
                                  "type"=>"asynchronous"
                                  )
                        );

View the source after its run and you'll see it converts it to use the
prototype.js object Ajax.Updater

If you change the type to synchronous, each div should load one after
the other, rather than all at once.
Hope this helps

Tim