I don't know about any CJK programs for Macintosh, though ... :-/

Apple's very own Language Kit.  The Japanese one runs $150.
Expensive, yes, but if you're a college student they may cost less.

No, there isn't a freeware version.  :-(.

They modify the OS to allow for the 2 bit Ascii table and come with fonts.
This allows you to write Japanese as well.. assuming you know the keyboard
layout.  I'd buy a Japanese keyboard as well to make things easier.

There is a separate language kit for Japanese and Chinese, though with the
right fonts you might be able to view Chinese under Japanese.  I don't know.

Then you need a Japanese "aware" program.

Netscape definitely is Japanese aware.  Most other e-mail programs are not.