How do you make it so the forum statistics(how many members are online,registered users, ect) are only visable to registered users?

No there is no way to do that. like you can have it not displayed but then it would be like that for all members,guest and even admins.. of course the admin can still see in the acp.

But you can allow you members the option to log in as hidden. but the remainder of how many members and post etc will remain there.

then you can always remove certain things out from the template edit if your useing phpbb2 or punbb.. but once again if you did that it would not appare for anyone.