If you assign a static address, there are a few more steps needed to get internet:
in a root shell:
route add default gw 'IP of router'
echo 'nameserver 8.8.8.8' > /etc/resolv.conf
NOTE: This is valid, assuming you have only one netork interface.
'8.8.8.8' is just for simplicity, you can use DNS server of your preference instead.