Lokkit ('lokkit or 'redhat-config-securitylevel') sets up iptables in RH. You'll want to check what's currently in there ('iptables -L'), and depending on how secure you want it to remain, either add a rule for Samba or remove everything ('iptables -F'). You'll want to check /etc/sysconfig/iptables as well, and clear it out if you're deleting everything.

See here for more info.