Someone actually needs to post something new and see if it works. They just upgraded the forums a week or two ago. My guess is that the path to where files get stored got changed which makes all old links broken, but new links will work. If it turns out new links don't work either, then it might be permissions on the images folder, instead.
OK... just tried uploading and got, "The attachments upload directory is not writable. Your attachment or avatar cannot be saved." Admins are going to have to do some work to make sure config is correct and that all folders exist with correct permissions.