Zushi,
my experience with this has been interesting so far. I used to use NS, and it was goofy enough trying to get, say, japanese pages to display correctly. But here's what I've accomplished so far with K-M, you can try it this way too, but I've noticed that some sites actually seem to crash the browser:
1. install the language pack.
2. search the internet for a suitable font and install it to your fonts forlder. I use MS Mincho since it seems to crash the browser less that MS Gothic does. In case you're wondering, these are japanese fonts and can be found at
http://www.ora.com/people/authors/lunde/cjkv-char.html
3. open 'prefs.js' with notepad or some other saves-to-text editor. add these lines:
user_pref("font.default", "MS Mincho");
user_pref("intl.accept_languages", "en-us, ja");
user_pref("intl.charset.default", "EUC-JP");
and save your changes.
4. go to a japanese web page and see if it works.
I may have left something out here, but if so, you might try Andrew's search above. (even if the K-M site does seem sort of oddly sorted-out and sometimes sparse on documentation).
Good luck
Buck