I'm guessing that you have a cable connection when you say "tv cabel", and I'm assuming you're using your iMac to post that message. Nexuiz does not say anything about DSL, it must be some other random thing on your computer. I don't know what, because it's an iMac, and those aren't usually prone to spyware and adware and stuff like that, so I've got nothing.
Ok, mabie I do. Try manually connecting to a server. Look one up at
http://delight.vapor.com/serverlist.php
Get the IP and port of one of the servers, and then open up nexuiz. Open up the console (shift+esc) and type "connect {IP}:{port}".
If it's your connection, it should output "connection failed". If not, you should see the game.