Trying to secure vBulletin with .htaccess - result: Internal Server Error!
 

I have been trying to get vBulletin to play nice with some additional security (for starters* a password restriction on the admincp directory. I have renamed it* but that is security through obscurity* which is not security at all.) However* all I seem to get are Internal Server Errors* and the only way I can fix the problem is to remove them (which* obviously* removes the security!)

Has anyone managed to get a SIMPLE user/password based .htaccess restriction working with vBulletin? I am on shared hosting (Pair.com) - so I do not have root access. But I would appreciate some info when it comes to hardening my forum against attack. I have searched Google and this site* but found nothing specific. Any takers?