Interesting. Neither do I, when I log out and browse as a guest / unregistered. Something seems to have been altered with the latest forum software upgrade, as it was working before. I note that it says on the bottom of the page that "You can upload attachments" to guests, so it is not that it isn't allowed, but rather that the browse button (and others) are missing. I'll look into it. In the meantime, I know it does work for registered members, so that is an option.
Okay, looks like this feature has been removed from the forums software. It looks like registration is now going to be required to post attachments. Here is my discussion with the people who develop the software: Guests and Attachments and Allowing Guests to Attach Images Short of making changes to the software, it is no longer possible for guests to make attachments. I dislike making changes beyond the default, as everytime the software is upgraded, I end up having to spend time reinstalling all the changes which can be better spent elsewhere.