The fastest way to get to Nozawa is via the Hokuriku shinkansen to Iiyama station. From there the Nozawa onsen liner bus service gets you up the the village in 25minutes.
Another convenient option is the Nagano snow shuttle service. This service runs every day during the peak snow season from both Haneda and Narita airports and can deliver you to Nozawa Onsen check out
The highway network in Japan is extensive and efficient. Getting from all major centers to Nozawa Onsen is easy. The toyota iiyama interchange is the closest access point to Nozawa from the Joshin-etsu expressway. But be sure to let us know if you are arriving by car- free parking in Nozawa is very limited in winter. See https://en.driveplaza.com/ for route maps and tolls.