Private leagues have the same chat box as public leagues. We've been blowing our chat winfdow up for over as week in NCAA. Are you thinking of an upgraded version or a different kind than the one in regular leagues?
You know what i think it is is if you're not in the league you can't participate in the league chat but the people in the chat can see your name in the window if you're on the league. I know i've seen many guys not in our league pop up in the chat window but no one has ever typed a message. When i go to another private league i'm not in i don't see a chat window option. So figuring that you're not in your league that's probably why you can't participate. Tomorrow jdb will be back on and clear it all up hopefully :)