Mac OS X Mountain Lion comes with Apache installed but not enabled. Here are the steps to re-enable Apache
1. Open the OS X Terminal (/Applications/Utilities/)
2. Create and open an Apache user configuration file named for your account in your favorite editor. I am using TextMate so I used the following command
sudo mate /etc/apache2/users/[username].conf
3. Copy the following text into the file that opens, but be sure to change the [username] text to the short name of your user account:
<Directory “/Users/[username]/Sites/”>
Options Indexes MultiViews
AllowOverride None
Order allow,deny
Allow from all
</Directory>
4. Save the file and close the editor.
5. Enable apache by typing
sudo apachectl start
6. Verify Apache is up by typing the following url into your browse
http://localhost/~%5Busername%5D
7. To enable the server even after subsequent reboots
sudo defaults write /System/Library/LaunchDaemons/org.apache.httpd Disabled -bool false
8. To disable the server even after subsequent reboots
sudo defaults write /System/Library/LaunchDaemons/org.apache.httpd Disabled -bool true
9. To be sure the files (and any others you may have configured) are properly accessible
sudo chown root:wheel /etc/apache2/users/*
sudo chmod 644 /etc/apache2/users/*
sudo apachectl restart
Dwain