Here is a rather robust iptables script..
I added the allow _only at the top of it just for you. It allows only incoming from the machine...cenrtain outgoing (and return based on outgoing..for updates and things like that) to any host is enabled..
modify to your hearts content.
*wink*
*note:It was a quick edit. make sure you modify the vars at the top to what you need.
http://cactuswax.net/~eliott/temp/iptables_regular.txt
rename to iptables.sh and run with
sh iptables.sh
test rules to make sure they are acceptable...
then
/etc/rc.d/iptables save
if you save before testing, even a hard reboot will not save you..