licensing issue

respected, i would like to implement the services of Freeradius server for one of our upcoming projects(Voip based application).i would like some information regarding : 1)i would like the server to interact with one of our clients programs and perform some some data retrieval tasks,ie the server recieves a request and will call an external program to perform the remaining tasks.i would like to know whether such an external program would come under GPLV2 or 3.The server performs the redirection the rest processing is performed by our application, the result will be notified by the server to the client. 2)can freeradius be used in windows (with cygwin) awaiting your reply. regards