Here is how I got this running on a VirtualBox guest quickly and easily.
First I update sources:
sudo apt-get update
sudo apt-get install python-software-properties
sudo apt-get upgrade
sudo add-apt-repository ppa:nginx/stable
sudo add-apt-repository ppa:nginx/php5
Then install the software:
sudo apt-get install nginx
sudo apt-get install php5-fpm
Next step is to enable fastcgi in /etc/nginx/sites-available/default
# pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
#
location ~ \.php$ {