Enabling .htaccess on OS X isn’t a very easy task. In order to that to work you will need, besides the loadmodule mod_rewrite.so and addmodule mod_rewrite.c, to change the httpd.conf and the website conf file. If you change only the httpd.conf it wont work and if you change only the site.conf it would not work.

You can definitely get more details on: http://www.clagnut.com/blog/350/

He says to use Override All on httpd.conf and Override AuthConfig on the other, but in our case we used All on both (with some limitations of who can create the .htaccess files).

Anyway the article is very well explained and was very helpful with our little battle at our OS X server.