Connect using FS2004
Select Multiplayer from the loading screen.
Alternatively, set up your flight and enter the cockpit, then from the FS2004 menu bar choose Flights >> Multiplayer >> Connect...
This will display the login dialog (shown below).
Enter your PilotID/Name and the Server IP address* and click Search.
Select the Air SeaTac Server in the list.
This will present the Server Password dialog box shown below.
* The Server IP Address is always available at Home | Online | Flight Server Details
Enter the Server Password* and click OK
* The Server Password is always available at Home | Pilot Centre | Flight Services | Help | Flight Server Details
(You'll need your Flight Services login to access this page)