Here is an American writer's article that puts Kurosawa's work into the context of Japanese film and mainstream film. (The questions are these: did Kurosawa "sell out"? Are his films more Westernized than Japanese?).
http://www.lardbiscuit.com/lard/kurosawa.html
These two sites discuss Nakadai's performance in a little more detail.
http://www.gotterdammerung.org/film/kurosawa-akira/ran.html
http://www.criterion.com/asp/in_focus.asp?id=15
Dr. Patrick Crogan's "Translating Kurosawa" examines the director's career overall but does not discuss Ran. Nevertheless, he makes useful points:
http://www.sensesofcinema.com/contents/cteq/00/9/kurosawa.html
For more information about contemporary Japanese film, see these sites:
http://www.csuohio.edu/history/japan/japan15.html
http://pears.lib.ohio-state.edu/Markus/Reviews.html
http://www2.shizuokanet.ne.jp/usr/onitsuka/English%20page.html
http://www.midnighteye.com/
http://www.sensesofcinema.com/contents/00/7/japanese.html
Here are sites on the history of Japanese film:
http://www.latrobe.edu.au/screeningthepast/reruns/rr0499/PUerr6.htm
http://www.greencine.com/static/primers/japan-60-1.jsp
More importantly, here are sites on Kabuki, a popular type of Japanese theater that may have influenced Ran. I hope that the video works! Ironically, samurai were forbidden from watching these types of plays.
http://www.ccds.charlotte.nc.us/History/Japan/02/bresn/bresn.htm
http://www.us-japan.org/edomatsu/tsukiji/frame.html
http://www.us.emb-japan.go.jp/jicc/spotkabuki.htm
http://video.google.com/videoplay?docid=6580589105119878240&q=kabuki
Other types of theater are Noh, Kyogen, and Bunraku. Noh is more tragic whereas Kyogen is comic. Bunraku is a type of puppet theater.
http://www.iijnet.or.jp/NOH-KYOGEN/english/english.html
http://www.artelino.com/articles/noh_theater.asp
http://www.hirohurl.net/kyogen.html
http://artscenecal.com/ArticlesFile/Archive/Articles2002/Articles1202/NohThea...
http://www.bunraku.or.jp/
http://www.sagecraft.com/puppetry/definitions/Bunraku.hist.html