Why is users able to post without login in?

Hi
In my site:
http://isha3ah.com/english &
http://isha3ah.com/arabic

Any user can post without having to login, is this a bug?.

say after entering a question on the bottom it says register and post, but when clicked it takes them to the register page, but in the meanwhile the question is aldready posted.
pls do advise what to do.

also let me know if i want to approve all posts before they start appearing on the site home page, what should i do?
rgds
Mira