I'm new to this whole multiplayer FS thing (I have FS 2004 COF) and I'm wondering what/where's the best place to get involved
Here are two.
http://www.vatsim.net/ More realistic.
http://zone.msn.com/en/root/cdrom.htm Casual flying if you can get into a flight.
If you're looking for more of a real-world multiplayer experience check out www.vatsim.net. They supply full and real air traffic control around the world (not 24/7, only when controllers are available). It certainly isn't for the faint of heart though.