We had a problem similar to this at one point that was our default gateway not being remembered after a reboot. Like you mentioned, we were obtaining the IP address and everythiing just fine, but could never get anywhere. Check to make sure your gateway is in fact getting set properly at boot time.
Type 'route' from the command line and take a look at what you see. It should be something like...
PHP Code:
[root@ns1 root]# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
65.65.65.0 * 255.255.255.128 U 0 0 0 eth0
127.0.0.0 * 255.0.0.0 U 0 0 0 lo
default 65.65.65.1 0.0.0.0 UG 0 0 0 eth0
We had to type the following in manually:
route add default gw GATEWAY'S-IP
That will probably be something like 192.168.1.1 depending on your setup.