3 hours 45 minutes is plenty of time to get into Narita Town and walk around a bit, EXCEPT, I don't know what effect 9/11 has had on getting back into the airport. I did this about a year ago. Read the first part of this thread:
http://www.flyertalk.com/pasttalk/ft...ML/001266.html

For things to do at Narita-town, go to the Narita Layover page:
http://net.saipan.com/personal/mike_...narita.html#do

Feel free to email me with questions.
Ed