Tim added an important fact which is mentioned indirectly in the NW 8 Release 
Notes.
Have a look at this section: "Strong authentication recommended between NMC 
Console and NetWorker server".
This assumes that it is also fact for the NW clients.

As new NW versions must be backward compatible , oldauth is still available - 
and it works. 
Just for curiosity i successfully backed up a Windows 2000 AS server with NW 
6.1.4 to the NW 8 server.

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