Unable to disable comments

Hey guys
Due to heavy spamming, I had to enable comment moderation. But while this has preventted spam-comments from appearing in the blog, I still have to delete a little over a 1000 comments every day and if this trend continues it’ll be 2000 by next week. So I decided to disable comments for a while and unticked the “Allow people to post comments on the article” option in the options-discussion page. But it has no effect on commenting. People can still comment and so can spammers. Does this feature not work at all? I am using 1.2-alpha-4 and I’d prefer not to upgrade. So if it does not work on 1.2-alpha-4, is there anyway I can add a little code to enable this disabling to work?
Thank you
Nish