The requested URL was not found on this server [closed]

This is really an Apache and OS X question and not specifically WordPress, but you may need to edit Apache’s httpd.conf file to allow .htaccess files to work on the one Mac.

Go to /etc/apache2/ (That’s for 10.6; Lion may be different) with the Finder’s Go >> Go to Folder… menu item (or via terminal) and edit httpd.conf and uncomment the instances of AllowOverride All in one or more <Directory ...> blocks. There may be several. Then restart Apache or reboot the Mac.

See http://akrabat.com/php/setting-up-php-mysql-on-os-x-10-7-lion/ for the whole process, including editing httpd.conf