I'll give you the settings to use.
To use what? Firestarter? KDE? IPTables?
For the Firestarter or Guarddog GUIs to configure iptables. As I'm sure your quite aware, by default, iptables blocks all inbound traffic. In otherwords, all ports are closed by default.
But it does not block outgoing traffic, which is why you use Firestarter/Guarddog to configure iptables, if you think you need to, or simply want to. (The link above (^^), discusses the need for a firewall on Ubuntu.)
If you're going to filter outbound traffic, you need to configure, in particular, the ICMP settings, so a person can run as "stealth" if they desire.
Like I said, if and when he gets there, I'd be happy to help him walk through the settings.
The following link is an overview of Firestarter. Guarddog is similar, since they're both are tied to iptables, which is standard on all modern Linux distributions. I believe there are some other GUIs in the repos, but I've never looked at them. I've been happy with Firestarter, and I assume Guarddog does what you want it to do.
http://firestarter.sourceforge.net/manual/wizard.php