There were some problems that arose from allowing everyone to access certain parts of the board. It was mainly a bandwith issue. Refer to this thread for more information on that
http://www.tfproject.org/tfp/showthread.php?t=71603
Also, from looking at your recent posts, you more than likely haven't been reviewed yet. Mods and Admins grant access and "promotions" after a review process. Hope this answered your question.
Edit: Also, check out this thread for the rules and guidelines. Section III should be helpful for your question.
http://www.tfproject.org/tfp/showthread.php?t=45061