version compatibility
You need to use Phusion Passenger version 2.1.1 or up.
configuration
This is the minimal apache2 virtual host configuration for a single site:
LoadModule passenger_module /path/to/module/mod_passenger.so
PassengerRoot /path/to/passenger/gem
PassengerRuby /path/to/ruby
<VirtualHost example.com>
ServerName example.com
DocumentRoot /var/rails/zena/sites/example.com/public
PassengerAppRoot /var/rails/zena
</VirtualHost>
The specific versions of path/to/... depend on your environment and how you installed passenger.