flush your iptables and see if your internet works then. try to disable then renable your interface. have you tried to unplug your ethernet cord, wait 15 secs, then plug it back in? if you can't even ping then there's a problem. post your dhcp lease file. i think it's inside /etc/dhcp3/ . we need to figure out if your internet isn't working because of a firewall or because of the driver or what. when you do
dmesg | grep ethernet
what comes back?