FAQ 119 (Can I edit/delete an entry in a community journal?) contains a link to FAQ 2 which ought to be enough for most users. For users who already know how to edit their journals using the http://www.livejournal.com/editjournal.bml method, this can be misleading though, as it's reasonable for them to assume that they don't need to read an FAQ that tells them how to do something that they already know about.
Would it be reasonable to add a note to the effect that using this method doesn't work for editing community entries, or something along those lines?