What protocol are you using? MSN, ICQ other?
There is this that details how the transfer works for MSN: http://www.hypothetic.org/docs/msn/c...e_transfer.php
It looks like the incoming port is 6891
As for how to add this to IPTables, I believe there is a GUI available, I am just not familiar with it.
The command line would be something like: `iptables -I INPUT -p tcp --dport 6891 -j ACCEPT`