Open the Control Panel, then click "Date, Time, Language and Regional Options"
Select "Add other languages"
Click on the "Install files for East Asian Languages" check box to ensure that the correct fonts are installed
In the "Text Services and Input Languages" box, click the "Details" button
Click the "Add..." button
In
the "Input language:" drop-down menu, choose "Japanese", and in the
"Keyboard layout/IME:" drop-down menu, choose "Microsoft IME Standard
2002 ver. 8.1"
Click "OK" there, and then click "OK" on the "Text Services and Input Languages" window that is left.
You
may be asked to put your Windows XP CD-ROM in the CD drive so that the
relevant files can be copied across to your hard drive
Reboot.
You should now see the IME icon in your task bar. Japanese will be an option when you click on it.