On my windows box I only need one port open, so I can open a socket connection to an AIR app and retrieve some status data occasionally. This is the only outside connection need.
How can I do this on windows 7, and secure it?
Open up the Advanced Firewall settings in Windows Firewall, highlight all active inbound rules and hit Disable Rule on the right pane. Now right-click on inbound rules and select New Rule. Follow the prompts to create a rule for your Adobe AIR app.
Could you not just configure the firewall to block all connections apart from the port you specify?
Go into Windows firewall -> Advanced and from there you can create new inbound and outbound rules blocking ports. Simply block all apart from the one you require.