Hi,
If you are logged in as a user with edit permissions on the forum page you should be able to edit or delete any post or thread, you should see a pencil icon next to the post or thread. If you don't see it I would investigate with Firebug to see if it is failing to load the image or is blocked somehow by CSS.
In a recent version we did add a setting to limit the amount of time that a user can edit their own posts, it defaults to one hour but is configurable from settings of the forum.
Recaptcha is still the best captcha available but it can be broken or spam my come from real users entering it. I generally advise don't allow anonymous posting.
Hope that helps,
Joe