In Netviz, select Tools->Import->Visio Masters... Navigate to the location of the .vsd file, and select open. Visio 5.0 or later must be installed on this system in order to complete the import.
There are a number of Visio masters that are available on-line from the manufacturers of the devices. Do an web search on "Visio masters" to find these.
How to import Visio stencils into Netviz
Are Visio stencils compatable with Netviz
Can netViz read .vsd files
(Legacy KB ID CNC TS15619 )