Are you using the Quake 3 multiplayer list? IF you have the pack that comes with team fortress, I would suggest installing team fortress just for its multiplayer interface. It is much cleaner and less confusing. Also, are you clicking "refresh list" or "get new list"? Also, is the source set to internet or mplayer? Make sure it is set to internet. I know you have probably tried all these, but sometimes it's the little things....

Mark