adding new AFCAD files

Presuming you already have the afcad files, put them in a folder inside your Addon Scenery main folder (rename it AFCADS or something). You might have to activate the new folder in the Settings menu before it displays.

Thanks for the help. Is there any difference between AFCAD and AFCAD2?

Basic plain english - A program to help design the layout of an airport for AI Aircraft use.

{r} AFCAD (AKA AFCAD1 ) - Airfield Facilities Computer Aided Design
From FS2000/2002 Program which enables users to "program" the invisible network of taxiways/runways/gates which AI aircraft use plus airport radio frequencies. The program works in a CAD environment enabling the user to "draw" the layout rather than tedious line by line manual coding. The resulting end product resulted in what's commonly called an AFCAD file or AFCAD's which are then put into FS.

The "R" in {R}AFCAD stands for Radius or Radii and refers to the methodology developed by PAI to enable users to "realistically" represent airport movements and gate assignment. Such assignments were a combination of the parking spot radius and the radius measurement set on the AI aircraft itself.
Basically {R}AFCAD was a complicated mess of many radii settings n model on spots specfic to airlines and the use of multiple "overlays" (a combination of a number of seperate AFCAD's to represent a single airport). The {R}AFCAD system wasn't particularly user friendly and therefore wasn't widely taken up, expect for hardcore AI enthusiasts. Most users just ending up plumbing for the extra parking and not worrying too much about the mess of airlines at the airports.

AFCAD (AKA AFCAD2) - Airfield Facilities Computer Aided Design

AFCAD 2 came into being with the arrival of FS9/2004. Changes in the sim itself meant AFCAD became much more powerful. The invisible AI network now became the visible, navaids could now be tweaked and a whole lot more.

The changes in the sim also meant the nightmare {R}AFCAD system of working was now obsolete. Lee Swordy combined with PAI (who beta tested AFCADv2) to develop a system for realistic AI airline operation which is much more user friendly and allows full customisation for hardcore users while maintaining the basic compatability for the average joe/out of box guy. The new system works on combination of Parking Spot radius, spot type, model radius and airline code.

The system was widely taken up, helped by it's ease of use and excellent documentation which comes with the AFCAD2 program itself which was a result of the close co-operation between Lee and PAI during the creation of AFCADv2.

AFCADv3??? - For FSX? As far as I'm aware Lee announced there'd be no further update after current FS9 version (v2.21) and no plans to create a version for FSX when it came along.