By my understanding, for clients (even the TSM server) are billed
as either

  a) server - billed by processor on each machine
  b) desktop - billed by machine, not processor

There is a break for desktop clients, and they are per client, not
per processor.  A desktop client provides no services to other
than the desktop user.  The desktop can run any OS, and is defined
more by function than by OS or type or number of processors.

For us, a desktop client seems to cost about half of what a server
processor license costs.

This info came from a telephone conference with IBM and our VAR, or
at least this is my understanding that came from that call.

We have no NDMP.  I did find the Exchange TDP is now licensed by
processor also.  And you must have a client on it to have a TDP, so
they bill you at least twice for the function. ... Such is life.