The National Institute of Informatics (NII) is located almost in the center of Tokyo. The guide map of NII is available from its Web site.
You can go from Tokyo Station to NII by taxi in about 10 minutes. NII is sited in the building called Gakujutsu Sogo Center (or National Center of Sciences), and its neighboring building, Josui Kaikan, is more famous. It might be better for you to show the taxi driver the Japanese map.
There are two subway stations near NII as shown in the guide map of NII. One is Jimbocho Station (S06/I10/Z07), whose A8 exit, located next to Shogakukan, Inc., is the closest to NII. The other is Takebashi Station (T08), whose 1b exit, situated next to Mainichi Newspapers, is the nearest. See also information presented by subway companies Tokyo Metro and Toei Lines. Their Web sites also provide instructions for using subways (which are complicated in Tokyo).
If you want to go from Narita Airport to NII directly, a simple way is to use Narita Express to get to Tokyo Station and then to take a taxi to NII (which will cost you more than 4,000 yen in total).
If you prefer an inexpensive way from Narita Airport to NII, the following alternative that uses two trains with one transfer might be appropriate:
|From||Narita Airport or Airport Terminal 2||Keisei Limited Express||50 min.||840 or 780 yen|
|From||Motoyawata (S21)||Toei Shinjuku Line||30 min.||310 yen|
Keisei-yawata and Motoyawata Stations are adjacent. It should be noted that sometimes Keisei-yawata Station is just called Yawata Station. You can see general information on Keisei Limited Express and its timetable. Trains on Toei Shinjuku Line depart frequently.