This has been asked many times before, PLEASE SEARCH NetPro for answers.
https://supportforums.cisco.com/message/1180953#1180953
Search "meetme + pin" and you'll get plenty of hits on the matter.
Bear in mind there is no real authentication unless you use CRS or MP, it won't check any list of participants or ask for a PIN.
It will just announce the user and the meet-me participants can choose whether to accept or deny entrance.
HTH
java
If this helps, please rate
www.cisco.com/go/pdihelpdesk
HTH
java
if this helps, please rate