iptables with serial connexion

Hi everybody,
I am trying to have a usefull connection through serial for my h3600 with my
slackware laptop but having problems since i'm quite new to both.

I can ping my ipaq from laptop but not my laptop from the ipaq.
As i suspected my iptables rule being responsible, i added this :
iptables -A INPUT -i ttyS0 -j ACCEPT
iptables -A OUTPUT -o ttyS0 -j ACCEPT
But it still doesn't work.

Does anyone have an idea ?

-- 
Mieux vaut allumer une chandelle que maudire l'obscurité.