You could use the global.asa file and keep a count in the Application object
Sub Application_OnStart
Application("ActiveUsers") = 0
End Sub
Sub Application_OnEnd
Application("ActiveUsers") = 0
End Sub
Sub Session_OnStart
Application.lock
Application("ActiveUsers") = Application("ActiveUsers") + 1
Application.UnLock
End Sub
Sub Session_OnEnd
Application.lock
Application("ActiveUsers") = Application("ActiveUsers") - 1
Application.UnLock
End Sub
Application("ActiveUsers") = currently active