Or, what was once THE page on it (my own).
Actually, it's become very easy now. The original page (at that URL) was far longer and more complex, though still simple when compared to Craig Oda's 1997 Japanese how to.
Aside from OpenBSD, where the README in the Japanese section says (or said when I last looked) that this might not work, Japanese in Linux and the BSDs has become almost trivial. (Actually, from what I understand, Xandros is still very difficult to get working with Japanese, which annoys those who buy the Asus EEE PC--but most people seem to buy it, take off Xandros and put something else on instead.)
Fedora (and CentOS) take it one step further. You can, in either one, just print a Japanese text file and have it come out properly. With other distros, and FreeBSD, one has to run it through paps, openffice or firefox first.
So, long winded answer as I feel philosophical, but the short answer was in the first line or so. Check out that page and it should work.
The one caveat that I've found in recent Fedora installs is mentioned on that page--the fact that sometimes, you have to manually add the hotkey for shift+space to get scim-anthy working properly. (It's explained in detail on the page.)
Wayne and I expect to see your answer in Japanese.