Wow, you are good! It works!!!
I created a shell script like the one here:
kinput2 -wnn &
and put it under ~/.kde/Autostart/. Now kinput2 starts automatically when I log in.
I just set LANG=ja_JP.eucJP and it works for me. Although I just tested it on Mozilla and OpenOffice. I am using KDE 3.1, too.