Darwin Ports useful commands

To update the ports
sudo port -d selfupdate

To search for and install a port, example program is fping
port search fping
sudo port install fping

More information can be found at
http://trac.macports.org/wiki/UsingMacPortsQuickStart

[Edit 19/07/2009]
This page looks like a very good resource on port commands:
http://guide.macports.org/#using.port