I'm not sure about yellow dog, but with RH8s security manager it had a bug that would always display the security level as high when you opened the security level manager. So even if you had it set to another level, it would always appear to be set to "high". However, even with it set to high, you should be able to browse the internet. So it might not be a firewall thing, but rather some kind of networking prob.
Easy way to check, turn off the firewall and see if you can ping remote hosts. Especially ping your gateway, a remote host by its IP address, a remote host by is hostname (like www.google.com
I'm not sure if yellow dog uses the redhat service command, but you should be able to use the following to turn off the firewall:
service iptables stop