Please follow the instructions,
>> At first, go to the below link & register there (free),
>> Then go to servers option in homepage.
>> In there, search your desired cod4 server like this,
>> After that, cod4 servers will be shown with ip address, port & country.
>> After that, click to join & then click to join server game option to play (Game Tracker Lite is Recommended! Download it from the attachment).
>> If you can't connect to the servers, use cod4 console to connect manually using ip address & port (console command e.g: connect 188.8.131.52:28966)