à Stief: you're fowarding the port to your machine in
http://192.168.1.1/Forward.htm ? I've had no problems with that. Don't forget to check the TCP and UDP protocols. Then in Limewire I go in Advanced and and change the to port (in Port and Firewall) you've determined before. Also note that disabling OS X built in firewall is a good idea, because it slows down the mac, plus you're behind a router wich is the best firewall you can buy. (anyway I'll never enable a firewall or add an antivirus software to a mac, it's a total waste of $$$ and processor).
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