Hi there Dan.
If you want to add traffic, here's what you need to do.
1) Download ttool202.zip from either SimV, no-nodes or avsim. Once you have, extract it to your main FS2002 folder and open it. Decompile the traffic.bgl file; this will create three new files called aircraft.txt, flightplans.txt and airports.txt.
2) Now, you must download a program which allows you to create flightplans easily. I myself find Yroute confusing, so I would recommend a fantastic program called AITE made by Josh Cooper. The file name is aitrafed.zip. With this tool, you can create many flightplans easily. With ttool202, you also get a file called 'collectairports2002.exe'. This collects all airports in FS2002 and makes a text file named the same. Delete the original 'airports.txt' that you decompiled from traffic.bgl and rename the new text file 'airports.txt'. This allows you to use every single one of the 22000 airports in FS2002 for AI Traffic, instead of the measly 1200 or so that have a tower.
3) Open up AITE.zip, and starrt creating flightplans. You will need AFCAD 1.4 to add parking spots to the airbases that do not have any so that AI traffic can actually operate there. When you are done, compile the 'flightplans.txt', 'airports.txt' and 'aircraft.txt' with ttools202.
Hope this helps,
Asda