The problem you're seeing, as least as it relates to 12.04 Server, is that the
networking service is not invoked and kept in a stopped state. I verified this on both my 12.04 servers with the following:
sysadmin@ubuntu-server:/$ service networking status
However, NetworkManager is running:
sysadmin@ubuntu-server:/$ service network-manager status
network-manager start/running, process 1479
and both servers are connected to the network, reachable and functioning fine.
Therefore, if you wish to reload a changed configuration file, you should issue
service network-manager restart
Verify your changed settings through
ifconfig. You may install any software you wish unless it requires a static IP address for some reason (very few do).