So you want FS2002 to use your 3rd party aircraft in it's air traffic huh?
There are a lot of utilities that deal with this, most will require you to have Traffic Tools so search a sim site and get it - but it is pretty confusing stuff, even with the helper apps...
Here is the easy way to deal with it. Use the TDecompiler.exe in Traffic Tools to extract traffic.bgl from FS2002, this will extract 3 files: aircraft.txt, flightplans.txt and airports.txt. Look at the file called Aircraft.txt (I have included my copy of this file for you to look at as a example - but don't use it because it reflects the planes I have), this is the planes AI uses for it's flights and it can be modified to use your 3rd party aircraft fairly easily...
Be sort of carefull to use planes of the same basic size when changing them (a 747 is not going to fit in place of a Cessna 172). But all you really need to do is copy the TITLE from your desired planes aircraft.cfg file and insert that in place of the name currently being used in aircraft.txt (see ATC.txt for a little info on the aircraft.cfg file if needed). Do NOT change the other parts of this file unless you know what you are doing. You can also add planes, but again you need to have a basic idea of how the 3 files used work together - NEVER alter the airports.txt unless you are SURE of what you are doing. But lets say you want to add 2 more planes to aircraft.txt, (you can do this by copying the info from a plane of similar size and changing the AC# to the next number in sequence plus changing the title to the aircraft you intend to use). However, FS2002 won't use them because they are never referanced in FlightPlans.txt - so what you need to do is pick a plane (AC#) from the original aircraft.cfg file and replace the NUMBER in FlightPlans.txt with the number of your additional plane (for lets say half of the flights, easy to do, just load FlightPlans.txt into notepad and then search for the original number). Lets say you want to use your new plane (AC#37) in place of AC#1. Search FlightPlans.txt and when you see AC#1 being used just change that to AC#37 and so on (but not for ALL the flights or AC#1 will never be used). In any case, once you have modified your files run TCompiler.exe and it will update FS2002 with the new info (be aware I take NO responsibility for you messing this up, so it is best to save copies of the original files TDecompiler makes in case you screw up bad ;>