I hate to tell you this, but: you're going to have to just learn iptables. You can look into a program called tinyfirewall . . . I dunno. It was the one that came with Mandrake for a while. Really, you're just going to have to learn iptables at some time because all a linux "firewall" is, in the sense you're talking about, is either an iptables front-end or an iptables configuration script. Either way you're going to need to know what is going on before you mess with those. You can, as I've been learning, have a pretty front-end but at the end of the day you need to know what is going on behind the scenes to properly use it.
That has been a pretty good tutorial so far, albeit a bit heavy for a n00b. It's not exactly a quick read, but it's solid.
You can also follow the links given above to manually shut down the services that are running causing the open ports. You'll most likely need to edit /etc/rc.inet1 and /etc/rc.inet2.
To steal from a previous thread of mine asking about firewalls:
A really basic script might be
iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP
iptables -A INPUT -p tcp --syn -j ACCEPT
iptables -A INPUT -p tcp -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A OUTPUT -p tcp -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
That should only allow programs you start on that machine to access the internet and should keep out connections from the outside.