Setting up Internet

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Sorry for the silly question, maybe I just haven't really been reading up
enough, but I have never really delved much into networks.  Here's my current
setup, all my systems are connected to a small home office router which is in
turn connected to a cable modem.  With my Windows machines I just plug a cat5
into an empty slot and it's automatically assigned an IP.  Some are setup as
static based on MAC and some not; regardless whenever it's plugged in it will
autodetect.  

During the FreeBSD installation it does not seem to pull any information down
when I choose DHCP, I foolishly did not enter in the required fields, & just
went on to setup XWindows.  Where do I modify my network settings?  What
command would I use?  Can anyone point me in the right direction for getting
my internet setup?