Thanks for the warm welcome and fast reply.
When plugging in the Spider-Board, the GHI NETMF Interface shows for about a second in the device-manager and disappears again.
The board is connected via a powered USB-Hub.
@John I don't know, it's been laying around for a few months.
Actually, it looks like the Spider is rebooting permanently (USB connection comes up and drops away after a second, comes up again.. and so on).
Update: I have disconnected all Extensions (except USB-Power) and now the GHI NETMF Interface stays visible.
In VS, it's now present named "EMX_Gadgeteer"
Update2: after reconnecting modulewise, it looks like the WiFi RS21 module is responsible for the boot-loop.