I have found that 'Gameranger' http://www.gameranger.com/
support CFS. I have played COD4 succesfully with Gameranger, but I have tried hosting a CFS game with a friend with no luck.It may be that you have to do the port forwarding thing with this particular game
. I have a room up if anyone wants to give it a try, if I am not there, leave a message saying when you will be back.
I will keep the room open daily for a while.