Open the Cluster Admin mmc. Your machines participating in the cluster will be/ should listed at the bottom, for each machine select the Active Group, in there it will list the state of the machine, online or off, that should tell you which machines are active.
That is and Active - Active setup and not a Active - Passive setup, what type of data is the cluster managing, which node has got a hold of the data at the moment, that is the one providing the service to clients