First make sure you have added SWBF2 to your Xfire game list. Then go to your Xfire game list, and then you can list the servers by hitting the button on the far right of the SWBF2 Icon/text and choosing browse servers. You click join a server, and it runs SWBF2, and then when you hit "join" for netplay it will instantly join the server you chose.
I still prefer replacing the swbf2.exe to this, but this may be something simple those who are computer challenged.