Playing with Call of Duty 2 v 1.3 with Mac & PC

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Hi to all
I've a Mac OS X and my friend Windows XP.
We would like to play on Call of Duty 2 version 1.3 with Remobo.
The Remobo connection with my buddy it's ok. But we can't see us on the list of "Local" server.
The multiplayer configuration of the game is (apparently) very simple; it doesn't request information such as number of IP or so on.
Any ideas?
Thanks in advance