Well, 2004 is still listed on the msn gaming zone you just have to go through the menu's a few different times/ways.

Another option is to do a google search for FSHostSpy by chocolate software.

Once you run the program it will give you a list of servers that are currently running. From there you search for a session that is 2002/2004 compatible whatever version of the sim you are running. Take the IP address and join up

Another option if you are indeed running 2004 is to head on over to Www.wspilots.com and join in the multiplayer fun there, it is very relaxed flying and usually no live atc just chat box and free flight...

Hope this helped!