Ive been all over looking for a way to disable the network adapter through M$ IP Helper routines.
For the majority of the code I\'ve been using this api: http://msdn
I don't know if there is a simple API to disable it. I think you might have to go through the device manager API. SetupDiSetDeviceRegistryProperty + SPDRP_CONFIGFLAGS + CONFIGFLAG_DISABLED looks promising.
There are also some suggestions here.