[kh99]

If the chat page shows up in "who's online", then you should be able to do a query to find out how many users are showing up as chatting (Edit: like Dave mentioned above). But that would only tell you how many people have looked at the chat page in the last 15 minutes (or whatever your session timeout is set to) and not necessarily how many users are active. The flash client probably knows how many users are active, but unless it has some kind of interface to share that info, then I'm not sure if there's any way to do what you want.