I remember reading somewhat recently that someone was producing an add-on for FS2k's ATC... I think it was some kind of an "expansion" to the original ATC, it let you choose other runways and opt for different flight levels, etc...Does anyone know the details about this add-on?

I believe you're referring to Radar Contact 3 - there's a forum for it further down right here... ;)

Click on the Radar Contact logo below to check out their web site & see if its what you are looking for...