For those of you that want to add to your airport but are using FSX, FSX Planner is a good answer. you can download it here:
http://www.zbluesoftware.com/fsxplanner/
Its interface is much like AFCAD, however it is still in a beta phase with little info on how to use it. If you have used AFCAD, then this will be a snap for you.

EDIT: I know this program was mentioned before, but I thought it needed its own thread