To post to the forum:

• You must not be in the "aggregated" view.  Select a forum to which you wish to post.
• You must be logged in to the website.  If you do not wish to register, you can use the anonymous login:
  
  User: anon
  Pass: password

Use the "login" link at the top right of this page to log in.

The Forums module was upgraded a while back.  Unfortunately it was not possible to move the old content into the new module.  You can still access the old forums by following this link.  You can no longer post in those forums however.