NAT iptables config

Hello.
I need some help to get azureus to work properly.
I understand there's a NAT issue, but can't fix it.
I have a linux box (no external router) and I set up NAT to share the
connection on my local network (beween my main pc and a notebook).
It works fine, but azureus does not.
The problem is that I need to open a certain port for azureus to use it.
I checked on https://www.grc.com/x/portprobe=80
that the azureus port (that's not 80, of course) was "Stealth".
I added this to the iptables script:
$IPTABLES -A INPUT -i ppp0 -m state --state NEW,ESTABLISHED,RELATED \
-p tcp -s $UNIVERSE -d $EXTIP --dport $AZUREUSP -j ACCEPT

and now the port is "Closed".
How can I open it in order to make azureus use it properly?
Are OUTPUT and FORWARD chains somehow involved?
I don't need to hand it over to the notebook, it's just supposed to work
with my main pc; so I think there's nothing about FORWARD, am I right?

Thanks :)
--
Guldo
www.giapponegiappone.it
Powered by Debian Sid

Sorry...
Looks like no firewall issue at all..
though I still can't understand why azureus stopped working all of a
sudden...

bye
--
Guldo
www.giapponegiappone.it
Powered by Debian Sid