The version 4.0 map uses Japan Digital Road Map Database published on March 2011 by Sumitomo Electric Industries, Ltd. This map is made for the car navigation.
You can search places in Japan if you know the "CHOME" address from the city category (Where To->Cities) on your GPS (Where To->Addresses will NOT work).
Search places from the City category
The version 3.0 is now possible to search by the Japanese 7 digits postal code.
Searching on Garmin Dakota
Postal code search on MapSource software
Navigation sample on Garmin NUVI. You can find the major street name on the map.
Navigation sample on Garmin Dakota