apt-cacher is a package proxy cacher for ubuntu/debian.

On the server:
1] sudo aptitude install apt-cacher
2] edit /etc/default/apt-cacher

AUTOSTART=1

3] Restart it

sudo /etc/init.d/apt-cacher restart

On the client:
1] Make sure you got the original /etc/apt/sources.list
2] Place on /etc/apt/apt.conf
Acquire::http::Proxy "http://<ip-address where apt-cacher is installed>:3142";
3] sudo aptitude update