I'm running Zonealarm free firewall on a windows notebook.
I noticed that when I updated the software on my Iphone 4(through Itunes) it was never successful unless I shut down the firewall

The same is true of Apple TV. The Apple TV device sees my notebook, but wont play any of the content (or Airplay) unless I shut down the firewall.

In the Apple help text, it suggests opening up port 3689 - however I cant find this option with Free Firewall - is it available?
Or if anyone has a better suggestion its much appreciated!