I'm not sure whether or not the DHCP server will tell your client about the router, or whether you're even using a router, but if you are try typing route -n just to make sure that a route is set up to go through your router with the destination as 0.0.0.0. So it should be something like:
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 0 lo
0.0.0.0 192.168.0.1 0.0.0.0 UG 0 0 0 eth1
if you don't have a line like the last one, and you are connecting to the net through a router, try typing
route add default gw 192.168.0.1
if your router's IP address is 192.168.0.1.
Hope it helps, it was worth a shot.
Edit: sorry the code tags are messing up a bit