The wiki used to be editable by anyone without a password. Then spambots started to vandalise specific pages, so we added edit passwords to those pages. Then a whole lot of vandalism went unnoticed because the changes didn't show up in the RSS feed, and we got annoyed and set an edit password on the whole thing.
You should be able to edit the wiki after logging in with your forum username and password. Some pages still have other edit passwords set on them. We're planning to remove those; if you are prevented from editing a page, come and complain here.
Logging in does not seem to automatically set the author name (at least in my browser), so please put in a name when saving your edits. I think it's kept in a cookie, so you only have to do it once in a while.