it sounds like you might be using network manager and as such the network is not coming up until you log in. If this is the case, to switch to a normal network setup (assuming eth0 and dhcp), you can do the following steps:
1. Stop and disable network manager (as root):
service NetworkManager stop
chkconfig NetworkManager off
2. Setup eth0: create /etc/sysconfig/network-scripts/ifcfg-eth0
3. Restart the network
service network restart
Now the network should be back up and should automatically restart when the machine is rebooted.