There are 2 cluster licenses in Power Edition 6.x. The Cluster Connection licesne will take the OS of the host (so if this is a UNIX NetWorker Server then the licesnes are for UNIX clusters).
To Calirify: A licesnes is needed for each physical node in the cluster. A license is not required for the virtual nodes.
With the example I gave earlier, if you wanted NT and not UNIX cluster clients, you would simply fill out the Host Transfer Affidavit and transfer the UNIX licesnes to NT.
Hope this helps.
mkeane