Simple and easy, just:
mkdir apt-cacher-ng && cd apt-cacher-ng
curl -LO https://raw.github.com/gist/1747868/Vagrantfile
vagrant up
Tail the logs perhaps?
vagrant ssh
sudo tail -f /var/log/apt-cacher-ng/apt-cacher.*
To use the caching box, determine your workstation's IP address and run the following on your Ubuntu/Debian node:
workstation_ip="xxx.xxx.xxx.xxx"
cat <<PROXY > /etc/apt/apt.conf.d/01proxy
Acquire::http::Proxy "http://${workstation_ip}:3142";
PROXY
quick update for the new version of vagrant
I also use this in my bootstrap script