Yup, pop on down into the Around The World Race/Multiplayer Events forum here.
http://www.sim-outhouse.com/sohforums/forumdisplay.php?f=6
Dave has a really good explanation in there on how to setup your firewall and internet connection to fly online on an FSHost server.
http://www.sim-outhouse.com/sohforums/showthread.php?t=27880
Basically, you do need to set up your firewall and router to allow certain ports to be open when you fly online. Otherwise data won't be passed between all the players in a multiplayer (online) session...which will cause problems with you or others not being able to stay connected to a flying session.
You can disable your firewall and open up your router (if you use one), but this is not recommended since there are so darn many nasties out there on the internet these days.
My Midnight Aircraft Parts Emporium FSHost server is open to all SOH members to use.
We don't use any formal ATC on there. It's just a "free flight" server and you can fly whatever and whereever you want.
Here is a link to a status page that will let you check to see if anyone else is online, what and where they're flying.
http://mape.gotdns.org/
Another status page that will show a Google Earth map of where the players are at...
http://mape.gotdns.org/user303.html
To connect to a multiplayer session...
Start up a flight in FS9 and then from the Flights menu select "Multiplayer" and then "Connect..."
You will see a dialog that allows you to set your player name and a place to enter the IP address.
For my MAPE server, enter mape.gotdns.org in the IP box and click the Search button. You should see a game session listed. Select it and click the Join button. This will connect you to the online session and also open up a chatbox where you can type text messages to other players.
That's it...you're connected.
If you are at the same airport as other flyers you should see their planes just like you would normally see AI traffic if you were offline. If you don't have the same planes that the other players have don't worry...they will appear in one of the default MS planes (or the last plane that you were flying).
That's a quick and dirty primer on how to connect to fly online with FS9. If you've got any more questions, feel free to ask! And we look forward to seeing you online. You too OBIO!!!