installing packages

Hello,
 
I just installed the 5.1 version a few days ago on an amd64
architecture. However, being new to the unix system of commands, I have not so
far been able to install packages such as mozilla firefox.
I looked through
the manual and tried to make things easy by using the PKG_PATH environment
variable. To fetch the requested package, I therefore first typed:
$ export
PKG_PATH=/mnt/cdrom/5.1/packages/`machine -a`/
and then:
pkg_add -v
mozilla-firefox
But the response I get at that point is the following:
file:/mnt/cdrom/5.1/packages/amd64/ is empty
Can't find mozilla-firefox
How
might I get around this?
 
Thank you,
Timothy Grison